Non-equilibrium polaronic quantum phase-condensate based electrical devices
10752513 ยท 2020-08-25
Assignee
Inventors
Cpc classification
H01L21/02565
ELECTRICITY
H10N70/823
ELECTRICITY
H10N70/257
ELECTRICITY
H01S5/34
ELECTRICITY
H01S5/3004
ELECTRICITY
H01L29/4966
ELECTRICITY
H01L29/66977
ELECTRICITY
H01L21/0262
ELECTRICITY
H10N99/05
ELECTRICITY
H01L21/02631
ELECTRICITY
G01R33/02
PHYSICS
B82Y30/00
PERFORMING OPERATIONS; TRANSPORTING
H10N70/253
ELECTRICITY
International classification
H01S5/30
ELECTRICITY
H01L29/49
ELECTRICITY
Abstract
Electrical devices operating in a range of 273 C. to 100 C. are disclosed. The devices include an insulating substrate. A UO.sub.2+x crystal or oriented crystal UO.sub.2+x film is on a first portion of the substrate. The UO.sub.2+x crystal or film originates and hosts a non-equilibrium polaronic quantum phase-condensate. A first lead on a second portion of the substrate is in electrical contact with the UO.sub.2+x crystal or film. A second lead on a third portion of the surface is in electrical contact with the UO.sub.2+x crystal or film. The leads are isolated from each other. A UO.sub.2+x excitation source is in operable communication with the UO.sub.2+X crystal or film. The source is configured to polarize a region of the crystal or film thereby activating the non-equilibrium quantum phase-condensate. One source state causes the UO.sub.2+X crystal or film to be conducting. Another source state causes the UO.sub.2+x crystal or film to be non-conductive.
Claims
1. An electrical device comprising: (A) an insulating substrate having a surface; (B) a first single UO.sub.2+x crystal or a first oriented crystal UO.sub.2+x film on a first portion of the surface, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film originates and hosts a non-equilibrium polaronic quantum phase-condensate; (C) a first lead comprising a first electrically conductive material on a second portion of the surface in electrical contact with the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film; (D) a second lead comprising a second electrically conductive material on a third portion of the surface, wherein the second lead is in electrical contact with the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film and wherein the first and second leads are not in contact with each other; and (E) a UO.sub.2+x excitation source in operable communication with the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film, wherein the excitation source is configured to polarize a region of the first single crystal or the first oriented crystal UO.sub.2+x film to activate the non-equilibrium polaronic quantum phase-condensate and determine an electrical conductivity of the first single crystal or the first oriented crystal UO.sub.2+x film, wherein a first state of the excitation source causes the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film to be electrically conducting, and a second state of the excitation source causes the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film to be electrically non-conductive.
2. The electrical device of claim 1, wherein the UO.sub.2+x excitation source applies a first voltage that is in a first voltage range to the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film when the UO.sub.2+x excitation source is in the first state, and the UO.sub.2+x excitation source applies a second electric voltage that is in a second voltage range to the first single UO.sub.2+x crystal or the oriented crystal UO.sub.2+x film when the UO.sub.2+x source is in the second state.
3. The electrical device of claim 1, wherein the UO.sub.2+x excitation source applies a light with an energy of 2.5-3.5 eV and with a fluence of 0.1-5 milliJoules/cm.sup.2 to the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film when the UO.sub.2+x excitation source is in the first state, and the UO.sub.2+x excitation source applies (i) a light with an energy of 4-5 eV with a fluence of 0.1-5 milliJoules/cm.sup.2 or (ii) no light to the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film when the UO.sub.2+x excitation source is in the second state.
4. The electrical device of claim 1, wherein, when the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is electrically conducting, an observable of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is detectable when the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is exposed to a magnetic field of 0.1 gauss or greater interacting with the magnetic moments of electrons participating in the polaronic quantum-phase condensate to modify the energy of a state in which they reside and thereby change a state of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film.
5. The electrical device of claim 4, wherein the observable comprises: a change in resistance between the first lead and the second lead, an absorption or emission of electromagnetic radiation by the first single UO.sub.2+x crystal or first oriented crystal UO.sub.2+x film, or a change in voltage between the first lead and the second lead.
6. The electrical device of claim 1, wherein the UO.sub.2+x excitation source applies a first laser pulse that is between 2.5 and 3.5 electron volts at the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film when the UO.sub.2+x excitation source is in the first state, and the UO.sub.2+x excitation source applies a second laser pulse that is between 4 and 5.2 electron volts at the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film when the UO.sub.2+x excitation source is in the second state.
7. The electrical device of claim 6, wherein the first laser pulse switches the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film from electrically insulating to electrically conducting in less than 50 femtoseconds.
8. The electrical device of claim 7, wherein the second laser pulse switches the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film from electrically conducting to electrically insulating in less than 50 femtoseconds.
9. The electrical device of claim 1, wherein the insulating substrate comprises an insulator layer on a substrate carrier.
10. The electrical device of claim 9, wherein the insulating layer comprises LaAlO.sub.3, CaF.sub.2, ytrrium stabilized zirconia, ZrO.sub.2, MgO, SrTiO.sub.3, SiO.sub.2, Al.sub.2O.sub.3, LiNbO.sub.3, NdGaO.sub.3, LaGaO.sub.3, KTaO3, BaTiO3, or MaGl.sub.2O.sub.4, and the substrate carrier comprises a polycrystalline material, monocrystalline silicon, or a semiconductor material.
11. The electrical device of claim 9, wherein the insulating layer comprises crystalline LaAlO.sub.3, CaF.sub.2, ytrrium stabilized zirconia, ZrO.sub.2, MgO, SrTiO.sub.3, SiO.sub.2, Al.sub.2O.sub.3, LiNbO.sub.3, NdGaO.sub.3, LaGaO.sub.3, KtaO3, BaTiO3, or MaGl.sub.2O.sub.4, and the substrate carrier comprises a polycrystalline material, monocrystalline silicon, or a semiconductor material.
12. The electrical device of claim 9, wherein the insulating layer comprises LaAlO.sub.3, CaF.sub.2, ytrrium stabilized zirconia, ZrO.sub.2, MgO, SrTiO.sub.3, SiO.sub.2, Al.sub.2O.sub.3, LiNbO.sub.3, NdGaO.sub.3, LaGaO.sub.3, KtaO3, BaTiO3, or MaGl.sub.2O.sub.4, and the substrate carrier comprises a metal.
13. The electrical device of claim 11, wherein the substrate carrier comprises aluminum, aluminum oxide.
14. The electrical device of claim 1, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film has a resistivity of less than 10.sup.4 .Math.cm when the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is electrically conducting.
15. The electrical device of claim 1, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is in the [111] orientation with respect to the insulating substrate.
16. The electrical device of claim 1, wherein x is in the range 0.05 to 0.35.
17. The electrical device of claim 1, wherein the first lead comprises a first metal and the second lead comprises a second metal.
18. The electrical device of claim 17, wherein the first metal is the same as the second metal.
19. The electrical device of claim 18, wherein the first metal and the second metal are the same or different and are each selected from the group consisting of gold, copper, aluminum, silver, platinum, iron, or alloys thereof.
20. The electrical device of claim 1, wherein the device is a superconducting field effect transistor in which the first lead is the source, the second lead is the drain, the UO.sub.2+x excitation source is the gate.
21. The electrical device of claim 1, wherein the UO.sub.2+x excitation source comprises an electrode that is separated from the first oriented crystal UO.sub.2+x film by an ionic liquid and the UO.sub.2+x excitation source applies a first voltage that is in a first voltage range to the ionic liquid when the UO.sub.2+x excitation source is in the first state, and the UO.sub.2+x excitation source applies (i) a second electric voltage that is in a second voltage range or (ii) no voltage to the ionic liquid when the UO.sub.2+x excitation source is in the second state.
22. The electrical device of claim 1, wherein a third state of the excitation source does not affect the conductivity of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film.
23. The electrical device of claim 1, wherein the first state of the excitation source is characterized by a first alternating current that is run through the excitation source in resonance with a state of the first single crystal or the first oriented crystal UO.sub.2+x film, wherein a frequency of the alternating current is tuned to be in resonance with a change of state within a condensate within the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film, and the second state of the excitation source is characterized by an absence of the first alternating current in the excitation source.
24. The electrical device of claim 1, wherein the UO.sub.2+x excitation source is electrically isolated from the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film by an insulator.
25. The electrical device of claim 1, wherein the excitation source is metal layer overlaying the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film.
26. The electrical device of claim 25, wherein the metal layer comprises more than 80 percent w/v aluminum, copper, silver or gold.
27. The electrical device of claim 26, wherein the metal layer comprises more than 80 percent w/v aluminum, copper, silver or gold is less than 10 nM thick.
28. The electrical device of claim 1, wherein the electrical device is a transmission line, and the insulating substrate comprises an insulator layer on a substrate carrier.
29. The electrical device of claim 28, wherein the insulating substrate comprises an insulator layer on a substrate carrier, the insulating layer comprises LaAlO.sub.3, CaF.sub.2, ytrrium stabilized zirconia, ZrO.sub.2, MgO, SrTiO.sub.3, SiO.sub.2, Al.sub.2O.sub.3, LiNbO.sub.3, NdGaO.sub.3, LaGaO.sub.3, KTaO3, BaTiO3, or MaGl.sub.2O.sub.4, and the substrate carrier comprises a metal.
30. The electrical device of claim 28, further comprising an electrical insulator that wraps around and electrical insulates the electrical device.
31. The electrical device of claim 28, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is at least a meter in length, and the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film has a cross-section of 0.05 mm.sup.2 or less.
32. The electrical device of claim 28, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is at least a meter in length, and the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film has thickness of less than 1000 nM.
33. The electrical device of claim 28, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is at least a meter in length, and the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film has thickness of less than 500 nM, the insulating substrate comprises an insulator layer on a substrate carrier, the insulating layer comprises LaAlO.sub.3, CaF.sub.2, ytrrium stabilized zirconia, ZrO.sub.2, MgO, SrTiO.sub.3, SiO.sub.2, Al.sub.2O.sub.3, LiNbO.sub.3, NdGaO.sub.3, LaGaO.sub.3, KTaO3, BaTiO3, or MaGl.sub.2O.sub.4, and the substrate carrier comprises a metal.
34. The electrical device of claim 28, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is at least a meter in length, and the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film has thickness of less than 600 nM and a width of less than 25 millimeters, the insulating substrate comprises an insulator layer on a substrate carrier, the insulating layer comprises CaF.sub.2 or ytrrium stabilized zirconia, and the substrate carrier comprises aluminum.
35. The electrical device of claim 1, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is electrically non-conductive when it has an electrical resistivity of 1.29 .Math.m or greater.
36. The electrical device of claim 1, wherein the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is electrically non-conductive when it has an electrical resistivity of 0.5 .Math.m or greater.
37. The electrical device of claim 1, further comprising a plurality of single UO.sub.2+x crystals or first oriented crystal UO.sub.2+x films on the first portion of the surface, the plurality of single UO.sub.2+x crystals or oriented crystal UO.sub.2+x films including the single UO.sub.2+x crystal or first oriented crystal UO.sub.2+x film, wherein each single UO.sub.2+x crystal or oriented crystal UO.sub.2+x film in the plurality of single UO.sub.2+x crystals or oriented crystal UO.sub.2+x films: (i) originates and hosts a non-equilibrium polaronic quantum phase-condensate and (ii) is in electrical contract with both the first lead and the second lead.
38. The electrical device of claim 37, wherein the plurality of single UO.sub.2+x crystals or oriented crystal UO.sub.2+x films comprises 5 or more single UO.sub.2+x crystals or oriented crystal UO.sub.2+x films.
39. The electrical device of claim 37, wherein the plurality of single UO.sub.2+x crystals or oriented crystal UO.sub.2+x films comprises 15 or more single UO.sub.2+x crystals or oriented crystal UO.sub.2+x films.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
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(27) Like reference numerals refer to corresponding parts throughout the several views of the drawings.
DETAILED DESCRIPTION
(28) Conradson et al., 2015, Possible demonstration of a polaronic Bose-Einstein(-Mott) condensate in UO2(+x) by ultrafast THz Spectroscopy and microwave dissipation. Scientific Reports 5, 15278, (hereinafter, Conradson 2015), which is hereby incorporated by reference, discloses ultrafast optical pump-time domain THz probe spectroscopy on UO.sub.2 crystals performed at Los Alamos National Laboratory. Conradson 2015 discloses that the quantum phase formed by laser excitation at 1.6 eV possesses extraordinary coherence throughout the host crystal in the form of periodic oscillations in amplitude that persist for hundreds of ps that and are observed through room temperature. Speculation, together with the results of Conradson 2015 indicate that the quantum phase both only forms after a certain threshold in terms of the number of photoinduced polarons and also saturates. This would be coherent exchange with another entity in the crystal and constitutes a signature of the proposed Bose-Einstein condensates. Conradson 2015 discloses electron paramagnetic resonance spectroscopy on UO.sub.2+x performed at University of Rochester. The spectra are unique and show that UO.sub.2+x hosts a number of different states with peculiar collective properties. Conradson 2015 concludes that the quantum phase formed by the polarons in UO.sub.2+x and UO.sub.2(+x) exhibits unique or at least extraordinary coherence and collective properties that can persist up to 300 K. Conradson 2015 speculates that coherence mechanism involves an excitation that is specifically an internal charge transfer reaction coupled to a phonon.
(29) The experimental results disclosed herein advance the understanding of UO.sub.2+x. In experimental results disclose herein, U M.sub.5 Resonant Inelastic X-ray Scattering, Non-resonant Inelastic X-ray Scattering, and O XAS on UO.sub.2+x were performed at, respectively, the European Synchrotron Radiation Facility, Advanced Photon Source, and Stanford Synchrotron Radiation Laboratory, and calculations were performed at University of Washington, Los Alamos National Laboratory, and University of North Texas. This combination of experiments that are now carefully calibrated by recourse to the scientific literature and to the calculations show that, in UO.sub.2+x, the gap in UO.sub.2 is being closed specifically by the formation of new states from the high energy, unoccupied electron levels and that there are even tails that may overlap with the occupied U 5f states to give a continues density-of-states as in metals. This is either unique or extraordinary. Disclosed herein, are ultrafast optical laser pump-photoemission probe experiments: with 4.7 eV excitation into the U 6d levels these immediately give the unoccupied UO.sub.2 density-of-states, but with 3.1 eV excitation in the U 5f levels these i give a continuous population of electrons through 3 eV above the Fermi level. Both of these results occur immediately within the 40 femtosecond width of the excitation laser pulse, with no intermediates, which is unprecedented. For 4.6 eV there are no hot electrons, indicating that the energy dissipation from the hot electrons also occurs immediately. For 3.1 eV the density of states on the high energy side of the highest occupied state does shift with increasing fluence, giving the appearance of some electron heating. This may, however, be the intersection of the plateau-like density of states that was not removed from the fit with the occupied states or may also be from relaxation from this unique type of electron spectrum. It is therefore likely that the heat transfer from the 3.1 eV state is also exceptionally fast. This is a characteristic of condensates, resulting from their superfluid properties. The lifetimes of these states are several picoseconds, and the relaxation appears to occur by loss of the photoexcited polarons, not decay of these states. Thus, the electronic states resulting from O-doping and photoexcitation appear to be the same state or similar; the polaronic quantum phase has many unique properties. The quantum phase identified here is the same as in the other experiments. The continuum of electrons created with 3.1 eV excitation must be metallic and conducting by our understanding of electronic structure in which metals contain partly filled bands. In fact, it would be a superthermal metal with an extraordinarily large number of carriers whose velocities would be maximum because they are continuous with and extend past the Fermi level. The postulated mechanism is consistent with these new experiments, as is the association with certain theories involving exchange between two states at the Fermi level and particular energy resonances.
(30) What is absent from Conradson 2013, Conradson 2015, and Conradson 2017 is any theoretical basis for the experimental results that could be used to help connect and explain them. Without intending to be limited by any particular theory, a theoretical basis for these experimental results is the concept of a non-equilibrium Bose-Einstein condensates, using excited phonons as the basis, although this could be more general, as first proposed by Herbert Frhlich in 1968. Over the last 14 years, work has been performed on laser excitation in quantum well materials that is now believed to produce a certain type of non-equilibrium BEC made of polariton-excitons. These can go to room temperature, but this is because they have almost no mass. In the last two or three years the amount of effort spent on these has grown because of possible applications in communications technology. Another type of non-equilibrium BEC can be made of magnetic excitations called magnons. The polaron condensates are totally different in that they contain mass, spin, and charge, and could therefore have many more applications than these others. The present disclosure proposes a phonon-based synchronization-resonance mechanism as a theoretical starting point. Theories from other topics are also used, such as the standard atom gas BECs, and high temperature superconductivity. UO.sub.2 appears to be a platform where these connections can be identified. The framework for consolidating and rationalizing years of UO.sub.2 into the framework of non-equilibrium condensates is a significant advance over the prior art and allows for considerations of how to use UO.sub.2 in a broad array of electronic devices. Some such electronic devices make use of the unique immediate transfer of energy among the different channels. Some such electronic devices make use of an optical switching time of UO.sub.2(+x), which could be related to the electric switching time, which appears to be at least 10-100 times faster than in any known material and could actually be even more, the metallic phase forms immediately. In addition, interpreting the unique electron spectrum with the known physics of conductivity, the conductivity could be higher than a typical metal by a factor of 1 to 100 million. The coherence, conductivity, magnetism, and switching of UO.sub.2(+x) all have potential applications.
(31) The systems and methods of the present disclosure further propose the use of UO.sub.2 in multilayers with other materials. For example, by coincidence, the lattice parameters of the (111) planes in UO.sub.2(+x) are almost identical with the CuO.sub.2 planes in cuprates, and thus a multilayer heterostructure synthesized from UO.sub.2 and overdoped LSCO, which could induce polarons in the UO.sub.2 without lattice defects while simultaneously doping LSCO into its superconducting state, is contemplated in the present disclosure. In fact, are any number of devices could be made from these combinations and could transform the properties of UO.sub.2 into or enhance those of its partner.
(32) Specific applications of non-equilibrium polaronic condensate (neqc) in UO.sub.2 are now disclosed.
(33) The conductivity of non-equilibrium polaronic condensate in UO.sub.2 has commercial application. Based on the electronic structure of the condensate that shows a superthermal metal, i.e., electrons partially occupying states continuously over an energy range orders of magnitude larger than in a normal metal, the correspondingly large number of carriers are expected to produce extremely high conductances that allow large amounts of current in small amounts of material to reduce the overall size and weight of any electrical component.
(34) Based on the combination of large numbers of free carriers, superfluidity, and coherence, the electronic structure of the non-equilibrium polaronic condensate in UO.sub.2 gives the conditions that provide the possibility of superconductivity at elevated temperatures. This superconductivity would have commercial applications. The superconductivity would exist up to the temperatures where these properties persist, which would be much higher than in a normal superconductor because the particles forming the non-equilibrium condensate that would also be or be related to the superconducting condensate exhibit an extremely high density because of their association with the close packed atoms of the crystal lattice and because they are in excited rather than ground states. Because the non-equilibrium polaronic condensate in UO.sub.2 is quite stable, its properties could be maintained by a very low energy input. This could be electrical or magnetic as well as by light. It is also possible that once it has been created it could be maintained even by thermal processes. The high conductivity could be used to reduce the size and weight of any electric component, including magnets and motors, the rapid switching time for ultrahigh frequency circuits, and these in combination with its microscopic magnetic properties for ultrasensitive magnetic sensors.
(35) In some embodiments of the present disclosure, the low dissipation in the superconducting or superthermal metallic states allows the non-equilibrium polaronic condensate in UO.sub.2 to be used for energy storage at energy densities much higher than current batteries and without the need for massive thermal insulation as with current superconducting technology.
(36) In some embodiments of the present disclosure, the metallic state of the non-equilibrium polaronic condensate in UO.sub.2 is switched on instantaneously by application of a laser pulse of the correct energy and fluence and the process reversed by the application of a laser pulse of a different energy. This serves as the basis for (i) optical switches with switching times near zero (e.g., less than 50 femtoseconds) and/or (ii) ultrafast detectors. In some embodiments, the switching can be performed electrically or magnetically thereby providing devices thereby providing electric switches with switching times near zero or at least limited by the other components of the device.
(37) Additional types of materials and circuits encompassed by the present disclosure utilize multilayers composed of UO.sub.2 containing the non-equilibrium polaronic condensate and other materials. The interaction between the non-equilibrium polaronic condensate and the carriers in the second material and the low dimensionality of the interface creates materials with additional unique properties derived from the coherence of the condensate. For instance, the coherence could be used for technologies derived from quantum interference such as metrology and other atomtronics applications.
(38) In some embodiments of the present disclosure, the non-equilibrium polaronic condensate is used for quantum computing. Assuming that the interpretation of experimental results as the coherent polaron quantum phase having condensed is correct, the requirements for superposition and entanglement have already been met by the observation of the transitions between the numerous electronic and magnetic states. The high temperatures, presence in an easily handled solid material, and control by electric and magnetic means would provide distinct advantages for qubits. Quantum computing with multiparticle condensates has been shown theoretically to have advantages of single particles in terms of speed, with the disadvantage that it should be more difficult to maintain coherence(45, 46).
(39) In some embodiments of the present disclosure, the non-equilibrium polaronic condensate is used for instantaneous (faster than the speed of light) quantum communications. Although faster than light communication is forbidden by the known laws of quantum mechanics and information theory, algorithms developed by others that circumvent these constraints have been proposed utilizing encoding schemes based on multiparticle systems. If these algorithms are correct then UO.sub.2 could be the enabling material. In such embodiments, a single non-equilibrium polaronic condensate would be created in two separate pieces of UO.sub.2 (e.g., two separate pieces of a UO.sub.2 crystal) by a coherent source such as a laser. These two separate pieces could then be separated and would react instantaneously with each other. Because the non-equilibrium polaronic condensate is composed of a large number of particles and itself has many different states it may be possible, unlike in current entangled systems, to process information via reading the state while maintaining overall coherence through the majority of its constituent particles. Another communications technology fostered by the quantum mechanical attributes of the condensate that would be a substantial improvement over existing single particle qubits is teleportation for secure communications.
(40) In some embodiments of the present disclosure, the non-equilibrium polaronic condensate is used for magnetic sensors and devices. The non-equilibrium polaronic condensate has a unique response to magnetic fields; it contains a number of both single electron and collective states that are controlled by the excess charge density and temperature. This is used in some embodiments for ultrasensitive magnetic sensors because of the energy changes in the energy levels induced by magnetic fields. It also provides a possible means for entanglement and improved qubits.
(41) High Electrical Conductivity: Application to Conductors for Power Transmission, Electronics, and Magnets.
(42) In some embodiments, the non-equilibrium polaronic condensate is used for power transmission, electronics, and magnets. Metals conduct electricity because electrons subjected to a voltage gradient can move through them via the unfilled states in the partially occupied band in which they reside, in contrast to insulators where the band is filled and they must cross a large energy gap to reside in empty states (
(43) The process is actually more complicated. Using the conceptually correct quantum mechanical model of Sommerfeld gives a different and more accurate description. Plotting the momenta of the electrons in an electron gas in a metal in three dimensions gives a sphere whose surface is the Fermi surface where the electron energies and velocities are at their maximum. Although all of the electrons are in motion, for any one with a particular momentum there is always another with the opposite momentum so the net current is zero. Applying a voltage displaces the center of the Fermi sphere in the opposite direction (
(44) The polaron quantum phase-condensate in UO.sub.2 formed from polarons resulting from O-doping and photoexcitation exhibits a density of states of the electrons that demonstrate that it is a metal or semimetal. Its current carrying potential of is obtained by comparing the numbers and energies of the carriers with those in a normal metal, such as copper that is often used as a standard. This was determined by optical pumping with a 40 femtosecond wide pulse of 3.1 eV light from fluences between 0.7 and 3.2 mJ/cm.sup.2 and measuring the energy resolved photocurrent coincident with the pump pulse and then via the time resolved integrated photocurrent through 24 picoseconds with relaxation times calculated through 7 ps(38). As seen in
(45) Although the energy resolved spectra with 3.1 eV pump energy were not recorded as a function of time, the time dependence can be inferred from the relaxation times of the energy integrated results (20, 38). At the higher fluences there is a very obvious fast relaxation whose rate decreases by more than a factor of 15 as the fluence is decreased, followed by a second slower one that changes only slightly with fluence and is close in value to the slow relaxation with 4.7 eV pumping that was both time and energy resolved. In combination with the fact that the shape of the photoelectron spectrum is the same at all fluences, only lower in amplitude at lower ones, it has been extrapolated that the low fluence photoelectron spectra are very close to or even the same as they would have been with time.
(46) These results for UO.sub.2 are unique and remarkable in that they are not explained by the known physics of this process. Similar to the pumping at 4.7 eV, the immediate t=0 photoelectron spectrum is the final, metastable state that relaxes back to the ground state over several picoseconds. However, instead of being the UO.sub.2 unoccupied states the photoelectron spectrum shows an energetically homogeneous electron distribution up through and possibly beyond the pump energy. This distribution is characteristic of the t=0 response of other materials except that for other materials it relaxes in a few tens to hundreds of femtoseconds and for UO.sub.2 the relaxation kinetics and fluence dependence demonstrate that this distribution is metastable and will be the state that persists through the relaxation. This can be partly understood by our study of the response of the Mott gap to O-doping that also produces charge inhomogeneities in UO.sub.2 that makes now UO.sub.2+x(20). The unoccupied states of the upper Hubbard band (UHB) of U.sub.4O.sub.9 and U.sub.3O.sub.7 that possess the same cubic, fluorite structure as UO.sub.2 are anomalous both by comparison with standard compounds U.sub.3O.sub.8, UO.sub.3, and UO.sub.2Cl.sub.4.sup.2 and DFT-LDA+U calculations that use the neutron diffraction derived structures that are also the minimum energy ones in these calculations. These structures are not the same as those derived from Extended X-ray Absorption Fine Structure (EXAFS) and X-ray pair distribution function analysis that show short, U(VI)-oxo type bonds(18), with these differences between the neutron and x-ray derived structures being indicative of tunneling polarons(27-29) as are present in high temperature cuprate superconductors(23-26). Oxygen K edge X-ray Absorption Spectroscopy (XAS) measurements show that the shapes of the spectra from these two mixed valence fluorite-structure compounds do not fit the two peak predominantly U 5f and 6d+O.sup.2p pattern (
(47) A superthermal metal is a new scientific discovery. Many of its applications will be derived from its conduction properties. Its conductivity can be compared against a normal metal using the microscopic mechanism described above. Because the electrons in the superthermal region are above the Fermi level their velocities will be even higher than those in a normal metal, which depend upon the width of the conduction band because that determines their energies that are counted from zero at its base. It is therefore conservative to assume that the velocities will be the same as the current carrying electrons in a normal metal and not adjust the conductivity for this. The relative conductivity of the condensate will therefore depend only on the fraction of electrons in the occupied region above the Fermi level. We can therefore calculate the number of electrons as the area of the densities-of-states that they occupy relative to that of the total band contains the two U 5f electrons. Using a peak amplitude of 70,000 and a FWHM of 1.4 eV (
(48) Since the power delivered by an electric circuit is P=V.sup.2/R=V.sup.2, an increase in conductivity, , increases the power and decreases the losses proportionately. Conductors, whether individual wires or patterned films could be theoretically reduced in cross sectional area by the this factor of of the superthermal metal divided by the conductivity of the Cu or Al that are the most widely used electric conductors. According to this calculation of the number of conducting electrons in partly filled states in proximity to the Fermi level, the value could be up to the factor of 10.sup.6-8, and at a minimum a still very significant factor of a minimum of 100 where conventional conduction would still occur prior to increased electron correlation. Alternatively, the reduced resistance could be used to lower the voltage for the same amount of current according to Ohm's Law, I=V/R=V. These advantages of the quantum phase-condensate in UO.sub.2 could be applied to electrical transmission lines, electric motors, electromagnets, and microelectronics.
(49) Electric Power Transmission.
(50) An electrolytic copper cable rated for 220 kV with a cross section of 800 mm.sup.2=has a resistance of 0.032 /km and a continuous current capacity of 800 A. Copper is considered to have one free electron that has a Fermi velocity of 1.610.sup.8 cm/sec, giving it 0.6.sup.8 current carrying electrons/atom at the Fermi edge. The quantum phase-condensate in UO.sub.2 has 0.03 current carrying electrons/atom, a factor of 50,000 higher. Conducting the same power as this Cu cable would therefore require only 0.02 mm.sup.2 of UO.sub.2, equivalent to a 40 mm wide 500 nm thick ribbon relative to the 32 mm wide Cu cylinder. The Cu in a 1 m long section of this cable has a mass of 7200 g, compared to the UO.sub.2 mass of 2.2 mg. The UO.sub.2 film would have to be supported on an appropriate substrate such as CaF.sub.2 or ytrrium stabilized zirconia, but this would also be quite thin to give it flexibility. Overall, the support structures for the UO.sub.2 would be combined with the insulation and give an overall mass and volume well under that for conventional Cu or Al. If the quantum phase-condensate was maintained by the current, discussed in a different section, then no additional circuitry would be needed, although periodic electrodes might be required to initiate it. If the quantum phase-condensate was formed and created by gating then a metal electrode would have to be added on one side of the ribbon, electrically and chemically isolated from the UO.sub.2, and a small voltage maintained. As noted previously, in contrast to the normal conduction induced by a voltage gradient that opens a channel only a few nm in height, the condensate appears to very quickly expand through a large volume of the UO.sub.2 host.
(51) Electromagnets.
(52) The most common way to generate a magnetic field for industrial use is by an electromagnet. The field an electromagnet generates, B, is, to first approximation, equal to NI/L, where I is the electric current passing through the conductor, N is the number of loops made by the conductor, is the magnetic permeability of the material within the loops, and L is the length of the magnet. The corresponding force for a circuit enclosing an area A is .sup.2N.sup.2I.sup.2A/2.sub.0L.sup.2. For a given permeability and cross sectional area high fields and forces are therefore obtained by high integrated currents (NI) and short lengths. N can be reduced to an equivalent length of a conductor, which for a circle of area A would be 2NA. Returning to the previous example, increasing the conductance of the current carrying material would reduce this total length of the conductor by the ratio of the conductance of the replacement material with that of Cu or Al. This is typically multiplied by the permeability of the core material, which can increase the strength by large factors. However, since this effect saturates the most powerful electromagnets do not use such cores. This length of the conductor would also go as the reciprocal of the ratio of the cross section areas, and for a material with a higher conductance and lower L from smaller N and cross sectional height there would also be an improvement from the reduction of L.sup.2. The field strength scales identically with the power transmission calculation, demonstrating that with sufficient improvement in the conductance the field strength produced by a large electromagnet, for example a magnet with a one meter circumference and Cu windings equivalent to 800 mm.sup.2 cross section, could be attained with the same 500 nm by 40 mm UO.sub.2 film, or a spiral path composed of 40 1 mm wide loops. Industrial strength magnets could be fabricated on a chip.
(53) Electric Motors.
(54) Electric motors would scale as their constituent electromagnets, so that their size would also scale as the ratio of the conductances of the new conductor with more conventional Cu or Al. Like electromagnets, the current carrying components of high power and high torque electric motors could be fabricated as a thin film on an appropriate substrate.
(55) Microelectronics.
(56) Microelectronics would be advanced by multiple characteristics of the UO.sub.2 quantum phase-condensate. Increased conductivity permits lower voltages and results in less heat, fast switching permits higher clock speeds, and higher rates of heat transfer allow heat to be removed, from both the UO.sub.2 and the other components.
(57) Ultrafast SwitchingApplication to Electronics and Detectors.
(58) Another unexpected property of the quantum phase-condensate is that, based on the t=0 photoemission spectra that are the final metastable states of the photoinduced polarons and do not show the energetically homogeneous electron distribution or mixing of the unoccupied states of the upper Hubbard band displayed in the spectra with 4.7 eV excitation in the ones from 3.1 eV excitation, the optical switching time must be much less than the 40 femtosecond width of the excitation pulse. Furthermore, the final state is dependent on the energy of the excitation, being in the supermetallic phase when it is 3.1 eV and in the UO.sub.2 insulating phase with the Mott gap when the excitation is at 4.7 eV. The combination of these results demonstrates that UO.sub.2 does not give the response to the ultrafast, high fluence pulse depicted in
(59) Possible High Temperature Superconductivity: Application to Conductors for Power Transmission, Electronics, and Magnets.
(60) Superconductivity is an electric current in which the movement of the carriers is without dissipation because they are in a superfluid state as a consequence of their condensation. With reference to
(61) With reference to
(62) A third mechanism is to create a heterostructure formed of layers of UO.sub.2+x with layers of a non-superconducting material. Interfacial superconductivity has been found in similar systems such as SrTiO.sub.3:LaAlO.sub.3, neither of which are superconducting or contain polarons, and in a monolayer of FeSe deposited on SrTiO.sub.3. U.S. Pat. No. 8,204,564 B.sub.2 discloses systems of this type based on the example of La.sub.2CuO.sub.4:La.sub.2-xSr.sub.xCuO.sub.4 the first compound is an insulator and the second has sufficiently high x to be metallic but not superconducting. The different chemical potentials promote charge transfer across the interface, with the accumulated charge at the interface that forms a two-dimensional electron gas being of a value such that the charges form Cooper pairs that condense to form the superconducting fluid. The use of UO.sub.2+x with its existing quantum phase condensate would facilitate the condensation of the carriers by the same mechanism as in [0084] and stabilize the condensate to higher temperatures.
(63) In some embodiments, the non-equilibrium polaronic condensate is used for energy storage, transfer, and conversion.
(64) Methods for Creating and Maintaining the Constituent Quasiparticles, Quantum Phase, and Condensate.
(65) Non-equilibrium systems can either be transitory or metastable, kinetically inhibited from relaxing to their ground state. Transitory ones require a constant input of energy. The identification of the UO.sub.2 system as non-equilibrium is more ambiguous than in other materials because our experiments have shown that doping with Oxygen substantially decreases the Mott gap that makes it an insulator rather than a metal, and may even close it to give an electron density of states with a constriction like a semimetal in proximity to the surface(20). UO.sub.2 is an insulator, but the electrical conductivity of oxygen doped UO.sub.2+x in the U.sub.4O.sub.9 or similar phase has not yet been measured definitely because of the difficulty of getting single crystals by oxidation of UO.sub.2 or fabricating thin films with this stoichiometry. The low conductivity may also be the result of the lattice defects resulting from doping it by adding oxygen. There is also the complication that this last occurred in low energy x-ray spectroscopic measurements that may have deposited sufficient energy to create enough photo excited states to give the quantum phase-condensate, which would be consistent with its non-equilibrium character. If the quantum phase-condensate is transitory, or transitory under certain conditions, it also facilitates using it as a switch in devices.
(66) Several methods are available to continuously input the energy to maintain the constituent polaron or polaron-like quasiparticles and the resulting quantum phase-condensate, some of which have been successfully applied to related systems. These include gating, an electric current, and excitation or induction via a resonant electric or magnetic field or radiation.
(67) Electrostatic gating is the process that occurs in, e.g., Field Effect Transistors, where a large voltage gradient is formed within a material by applying a voltage to a conductive gate in contact with or adjacent to it and that is electrically isolated and chemically isolated or inert. A negative potential causes electrons to move away from the interfacial region, giving an excess of holes at the interface and thereby doping a plane of the material a few nm thick, or vice versa. This process emulates photoexcitation that produces electrons and holes without introducing any defects in the lattice. Under the reasonable assumption from the structural measurements that find U(VI) associated with the quantum phase-condensate that must have originated in aggregation and disproportionation of the U(V) holes and the instability of aggregated U(III) in U oxides, a volume enriched in U(V) should therefore give the electron DOS found by the time resolved photoemission measurement. It has been found in TaS.sub.2 which also exhibits multiple states including a metastable hidden state, that the state can be selected by the amount and direction of current(56), and by combinations of heating and photoexcitation below the fluence where the electron order is completely melted(61). It could therefore be expected that switching between the ground insulating, excited insulating, and excited superthermal metal states can be selected analogously.
(68) An effective means for accomplishing this in the laboratory is not, as in a metal oxide semiconductor FET, with a metallic electrode separated from a semiconductor with an oxide or other dielectric layer making an all solid device that must be fabricated by deposition methods and may have poor contact at the interfaces and that has a maximum carrier density of 10.sup.13. Rather, it has recently been discovered that carrier densities larger by a factor of 100 times or more can be attained by using an ionic liquid as the polarizing or voltage transmitting medium(62-64).
(69) Although a substantial improvement, ionic liquids nevertheless are far from perfect as gates. Although their fluidity allows them to make close contact with any material and avoid epitaxial strain and mismatch at the interface, it also results in disorder in the arrangement of charges on the microscopic level. It has also been discovered that using ionic liquid gating to effect insulator to metal transitions in oxides(65) causes not only charge injection but also the removal and addition of O(66, 67). Since UO.sub.2 is highly reactive towards the removal of small amounts of O and especially oxidation, gating would probably not be useful in injecting charge while maintaining a fixed U:O ratio to emulate photoexcitation-induced charge separation and polaron formation with no lattice defects. There is, however, a recent advance in this field that would allow this. The Goldhaber-Gordon group has found that a 0.5-1.5 nm film of inert boron nitride placed on top of the materials to act as a chemical barrier between the ionic liquid and the material prevented the oxidation of gated Au. It also enabled carrier concentrations in SrTiO.sub.3 (STO) into the two-dimensional electron system region of around 410.sup.13 carriers/cm.sup.2, substantially higher than in SrTiO.sub.3 without the film and comparable to those in the LaAlO.sub.3:SrTiO.sub.4 system. This increase was postulated to result from a combination of separation from the charge disorder in the electrolyte and the retention of the O because of the impermeability of the BN film(42), with reference to
(70) In contrast to gating that creates free carriers in a small volume at the interface where the gate voltage is applied, the application of an electric current driven by less than 5 V has been shown to close the Mott gap to give the metallic state in oxides (43, 56, 68, 69), such as VO.sub.2 (
(71) Fabrication of Heterostructures with Charge Reservoir Domains.
(72) Almost all quantum materials are activated by chemical doping, e.g., substituting ions with difference charges or adding nonstoichiometric amounts of O or another anion. The transition metal that is central to its properties therefore occurs in more than one valence, making a mixed valence compound. These charges and spins can order in a variety of ways. UO.sub.2 conforms to this description, with the interesting properties accruing to O-doped UO.sub.2+x or photodoped UO.sub.2 when the U is a mixture of (IV) and (V), or (III), (IV), and (V) valences. As already described, the problem is that the adventitious O forms defects in the lattice that disrupt transport and other properties that require a periodic structure by pinning the charges at the defect sites. This is universal amongst these compounds, e.g., substitution of the Cu with other metal ions in the CuO.sub.2 planes in cuprates destroys the superconductivity at a few atom-% level. The doping in these materials, often by a combination of non-transition metal ions or different valences such as LaSr/Ba and non-stoichiometric amounts of O, is accomplished without disrupting the CuO.sub.2 planes through their layered, multidomain structures (
(73) UO.sub.2 with its simple stoichiometry and uniform cubic structure is not amenable to chemical doping. UO.sub.2+x is mixed valence, but disordered, which may be why it remains an insulator despite the near closing of its Mott gap. The addition of alkali metal or alkali earth ions gives the ternary uranate compounds, which could be susceptible to doping. However, these also form cubic rather than layered structures so that the other cation is combined with instead of separated from the U. The structures of U in its higher (V) and (VI) valences are layered, but these do not contain sufficient electrons for the quantum phase. In addition, the fluorite and the layered structures do not combine despite the similarity in structure of their U (111) planes, U.sub.3O.sub.8 always separates on the macroscopic scale from U.sub.3O.sub.7.
(74) An alternative is to form artificial structures that emulate the cuprates and related compounds by thin film fabrication methods. UO.sub.2 is easily deposited on a number of substrates, including CaF.sub.2 as well as more complicated ones such as LaAlO.sub.3 and ytrrium stabilized zirconia. Either a substrate or a capping layer could be selected that has a structure similar to that of UO.sub.2 but that could be made non-stoichiometrically with a charge deficit and an electrochemical potential high enough to remove electrons from U(IV) to generate a layer of a mixed valence U(IV/V) material. The LaSrAlO.sub.3 system is one example, where the La:Sr ratio dictates a particular O stoichiometry that, if exceeded, will withdraw electrons from the material to which it is coupled. If the energy of the O hole in LSAO is greater than the O defect in UO.sub.2 the charge but not the O will be transferred. Coincidentally, the CuO.sub.2 planes of cuprates are only a few percent different in size from the U (111) planes of UO.sub.2, making them candidate substrate materials (
(75) Resonant Excitation and Induction.
(76) The underlying theory and mechanism for the quantum phase-condensate based on the finding of U(VI) involve an oscillating electric dipole, as prescribed by the original theory for a non-equilibrium condensate(6, 7, 21, 72). Specifically, we have proposed that its origin is the coupling of a phonon that synchronously drives charge transfer and the speciation-geometry change as the result of the dynamical change in the separation between the (111) U planes(19). Alternatively, there could be exchange between two coherent states that are the different chemical species connected by the charge transfer, in which case the exchange would not need to be synchronized by the phonon. The time domain spectroscopy, both with optical reflectivity(18) and THz transmission probes(19), both show strong coherence signals whose frequencies do not correspond to any of the phonons of UO.sub.2. They must therefore originate in the quantum-phase condensate, either as phonons or as coherent exchange. If the former, then their low frequencies, 1.8 THz and 12 GHz, imply that they are synchronized motions over large volumes of the material. If the latter then these would be the energy differences between the coupled states. Because the exchange between the states involves the motion of charge, either as charge transfer between ions or, if the charge transfer is incomplete, a large dipole, it would be possible to excite it directly via an alternating electric or possibly magnetic field oscillating at the same frequency to resonantly drive the motion and exchange, initiating and maintaining it. These frequencies are sufficiently low so that it could be accomplished by an AC current in a wire or other geometry conductor in proximity to the UO.sub.2.
(77) Control by Strain.
(78) Another method that has been used to modify and control insulator to metal transitions and relative phase stabilities in correlated oxides and related materials is strain imposed by fabricating a film on a substrate selected to have an epitaxial mismatch or by bending a thin film on a substrate(57, 58, 73-77). This method could also be applied to tune and control the relative stability of the quantum phase-condensate and ground state in UO.sub.2 and of the various states of the quantum phase-condensate.
(79) A UO.sub.2+x crystal or a first oriented crystal UO.sub.2+x film on a first portion of the surface, where the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film originates and hosts a non-equilibrium polaronic condensate that can be used in heterostructures to make superconductors, normal and exotic, and interfacial, and also non-laser coherent light sources, magnetism, qubits, and heat pipes via the superfluid thermal conductivity.
(80) Atomtronics and Sensing.
(81) Analogous to electronics, atomtronics is the science and associated technology resulting from controllable matter waves(78, 79).
(82) As with optical and magnetic computing, it would be based on devices that are the matter or atom analogs of transistors, diodes, beam splitters, etc. The three requirements for devices utilizing atomtronics are (i) a set of atoms that possess coherence and superfluidity, as in a Bose-Einstein condensate, (ii) a method for controlling their positions, and (iii) a method for controlling their energies, both kinetic energy and states
(83) The use of a polaron condensate or coherent quantum phase with superfluid properties easily meets all three requirements. In contrast to an ultracold dilute atom gas condensate whose constituent particles are neutral and coherence is extremely fragile, polarons are easily manipulated on the basis of their charge and magnetism and, although their quantum phase-condensate is separate from their host lattice, they are nevertheless confined to volumes that have the correct composition and structure. In addition, because the polaron quantum-phase condensate is non-equilibrium, its coherence extends to easily attainable temperatures, even ambient temperature in some experiments. Its existence in a crystalline solid instead of an ultra-high vacuum greatly facilitates the design and fabrication of the necessary circuit components and devices. The detection of the polaron currents and potentials is easily done by monitoring emission, charge, or magnetism either directly or via spectroscopic probes. Applications include metrology, based on the short wavelengths of atoms vs. electrons and light, and metrology derivatives such as gravimetry.
(84) Response of the Mott Gap to O Doping and the Static CPQP.
(85) The O XAS of cubic UO.sub.2 and, for comparison, layered U.sub.3O.sub.8, UO.sub.3 (40, 80-82), and Cs.sub.2UO.sub.2Cl.sub.4 (83) display two peaks below the continuum (
(86) The occupied states, consisting of the O 2p and the U 5f states of the lower Hubbard band (LHB) just below the Fermi level (88), are probed by valence-to-core 3d5f RIXS at the U M.sub.5 edge (89) measured at 3552 eV (
(87) Magnifying the DOS and spectra around the Mott gap provides more detail (
(88) O-doping of UO.sub.2 to UO.sub.2+x therefore substantially reduces or possibly even bridges the Mott gap principally by shifting the UHB downwards, with a small but finite DOS at the intersection with the LHB that increases rapidly with increasing energy (
(89) Time-resolved photoemission was performed (38) concomitant with the excitation pulse with a time resolution of 40 femtoseconds at excitations of 1.6, 3.1, and 4.7 eV that would be transitions from the U 5f state into, respectively, the gap, the unoccupied U 5f and the unoccupied U 6d states. The fluences of 0.13-0.51 mJ/cm.sup.2 at 4.7 eV correspond to 0.002-0.006 excitations/U in the top 1 nm, comparable to the 0.009 excitations/Ta for TaS.sub.2 that induce the insulator-metal transition (30)). As with the other optical pump experiments performed on UO.sub.2(=x), these measurements also gave highly unusual results. The prominent features in the 4.7 eV excitation spectra are the Mott gap and the front edge of the unoccupied UHB 5f states of the static UO.sub.2 DOS (
(90) The t=0 spectrum with 3.12 eV excitation, with fluences from 0.7-3.2 mJ/cm.sup.2=0.015-0.07 excitations/U in the top nm, gives the converse DOS (
(91) Although this t=0 spectrum shows the expected metallic state (30, 101) typically observed in oxides (102), its extended energy, relatively flat DOS, and the stability implied by its extended fluence independence and association with the slow lifetime resemble the behavior of graphene (103). This is significant because, although this common response could be coincidental, the present disclosure shows that the DOS of O-doped UO.sub.2+x also resembles that of graphene in that the shift of the UHB and consequent closing of the Mott gap in UO.sub.2+x causes the DOS to descend to a narrow constriction at or near the Fermi level followed by a rapid increase immediately afterwards into the unoccupied states. Another similarity specific to the excited states of both is that thermalized electrons fill in this chokepoint off of the leading edge of the valence band as in metals, bridging the occupied and unoccupied states (
(92) The t=0 DOS produced by 3.1 and 4.7 eV excitation are opposites (and 1.6 eV gave no effect (38)). The former promotes electrons into the unoccupied states of the CPQP that forms concomitantly, the latter into those of the static UO.sub.2 structure. That this is not a fluence effect is demonstrated by the lifetimes (38) and the complete absence of the 5f UHB feature with 3.1 eV. Energy dependence in the initial response to intense fs optical pulses is antithetical to the current depiction of the photon impulse promoting hot electrons into a continuous, nonthermal energy distribution (30, 101). This result for UO.sub.2 is, however, obligatory since excitation at these energies also gave different results when probed by reflectivity that gave the CPQP when excited at 3.1 but not 4.7 eV (18), just as it also gives the CPQP-type result here.
(93) Discussion
(94) Relative to the minor modifications of the LHB, the substantial extension of the DOS from the edge of the UHB into the Mott gap indicates the formation of novel states separate from and not just perturbations of the UO.sub.2 host. These results therefore corroborate this same interpretation of our previous experiments about the presence of the CPQP. Although the shape of the occupied states after 3.1 eV photoexcitation (
(95) In addition to the previous findings of greatly extended lifetimes and coherence coupled to non-UO.sub.2 static states, what is observed here are that electrons with energies 2-3 eV above the Fermi energy persisting for an extraordinary 6-9 ps or more at ambient temperature (38) (and possibly s below 60 K if this is the same state observed in the optical pump-reflectivity probe experiments (18).) This can be understood for the static UO.sub.2 5f states obtained with 4.7 eV excitation because, as has been posited (38), relaxation requires crossing the full Mott gap (
(96) The quasiparticle non-equilibrium, exciton-polariton and phonon condensates form because relaxation is inhibited. The excited quasiparticles accumulate in the first state above the bottleneck to give the nonthermal population distribution that subsequently attains coherence. Underlying these extended lifetimes are specific resonances. For phonons it is the proximity of the excited phonon energy with the chemical potential (6, 105), for exciton-polaritons it is the proximity of the exciton and cavity photon energies around k=0 and their avoided crossing that creates the minimum in the lower polariton band (13), and for the dilute atomic gas fermion-diatomic molecule boson systems it is the matching of the continuum of the fermionic potential with the energy of the molecule that turns on their exchange via the Fano-Feshbach resonance (32, 60). A resonant effect has already been demonstrated in UO.sub.2 by the excitation energy dependence of the coherence, lifetimes, and the formation of the photoexcited CPQP.
(97) The role of resonance and the microscopic themes in non-equilibrium Frhlich BECs and the specific contributions to UO.sub.2 are elucidated by examination of the generic potentials of two state systems. The polarons on the apical O in cuprates tunnel between the two halves of a symmetric, degenerate, double well potential because the two structures involved are identical (24-26, 28) (although it is possible that the polarons in the CuO.sub.2 planes are more complicated (106)). An asymmetric double well would have been superfluous because of the assumption that the functionality originates in the ground state phase at all temperatures. In contrast, the two species involved in a non-equilibrium condensate are non-degenerate by definition, resulting in an asymmetric potential composed of the ground and excited quasiparticle states (
(98) For the UO.sub.2(+x), CPQP the open channel is the unpaired spin (triplet), weakly paired, fermionic U(IV,V) polarons in the U.sub.4O.sub.9-like domains that have been shown (108, 109) to be more stable than isolated polarons, which would be the continuum state. The bosonic U(IV,VI) excited singlet state is the strongly paired closed channel. Relaxation is inhibited and the nonthermal population and condensation are favored when the chemical potential is near the energy of an excited phonon (6), although this derivation is not specific and should apply equally well to any system with oscillating dipoles. The chemical potential in UO.sub.2 will be in the Mott gap, defined as midway in a semiconductor or insulator. Since the states of the CPQP span the gap, or at least the measured DOS is large at the midpoint of the calculated gap for U.sub.4O.sub.9, this condition is met. Insofar as polarons maximize the atom displacements and polarizability they also fulfill this criterion for strong condensation enhancement. In addition, the energy of the U.sub.4O.sub.9-like U(IV,V) cluster has been calculated to be 2.2 eV below that of the separated U(V)O defects that would be the continuum-free polaron level (90). Remarkably, this is almost exactly the difference between the centers of the spectral features that would be the occupied U 5f(
(99) These new results in combination with previous ones provide details on the underlying mechanism in energy-momentum space that complement the real space scenario, indicating that it is direct and does not involve suppression of competing orders despite the antiferromagnetism of UO.sub.2 (19, 110). The x-ray and neutron structure measurements (18, 111) have identified the specific tunneling polarons that, because they alternate between the open channel fermion and closed channel boson states via the disproportionation reaction 2 U(V).Math.U(IV)+U(VI), define the asymmetric double well. The persistence of the condensate to high temperature is therefore a natural consequence of its origin as an excitation. Coherence throughout the entire domain is attained through synchronization of the electron transfer and correlated rearrangement of the O ions that constitute this reaction via the relative stability of the U(IV,V) species at the short U-U distances on the compressive and U(IV,VI) ones at the long distances on the tensile side of the [111] phonon. This phonon is special, also being implicated in stress relief caused by various defects (36, 112). The long range force for UO.sub.2(+x) is therefore at least partly elastic instead of solely Coulomb. Specific to UO.sub.2 and its absence of an insulator-to-metal transition; UO.sub.2 differs from related materials in that the fluorite structure does not have a preferred orientation for adding O so that U.sub.4O.sub.9 is three dimensional. The layered U(IV)-(VI) structure that is the excited state displays the alternative valence that constitute a charge-density wave, inverting the normal energies of the insulating and metallic states. In addition, another possible reason for the differences in the response to different excitation energies is that the excited state produced by 3.1 eV but not 4.7 eV excitation is coupled to the U [111] phonon, analogous to phonon-driven enhancement of electron correlation in cuprates (113) and has recently been postulated for C.sub.60 (114).
(100) The electronic structure of the CPQP maps directly onto this real state model. The CPQP is a different species, not the minor perturbation of UO.sub.2 predicted by the calculations, with only the states above the Fermi level affected because it is an excited state of UO.sub.2. Its wide dispersion would result from the UO bonds that, like the U-U pair, would have the almost continuous range of bond lengths over a minimum of several tenths of an A, augmented by the mixing of the two strongly coupled parent states via the tunneling (28). The tunneling would be another signature of a condensate, since it is far too long a distance for conventional tunneling but small within the superfluid (115) tunneling regime. In addition, the energy overlap of the ground U(IV,V) and excited U(IV,VI) DOS indicates that the dynamic exchange of their local atomic structures is also the coherent exchange between their electronic states that are separate at the Fermi level. This exchange enhances condensation in two-band descriptions of exotic superconductivity (116, 117). Thus, in UO.sub.2 the phonon that impels the hopping of the charges also promotes the coherence and resultant condensation, which is the opposite of it disrupting competing orders (113, 114, 118). This coherent exchange, as a Fano-Feshbach resonance that amplifies exotic BCS (33, 34) and fermionic atom-molecule gas BEC condensates (60, 119, 120), would be the origin of the coherence of the two states or their combined single one.
(101) Accepting the evidence that the CPQP in UO.sub.2(+x) is a non-equilibrium Frhlich-type BEC, the question is whether it will have in common the properties of other condensates and also if it will exhibit novel ones. Although the extended lifetimes of the states after photoexcitation relative to other materials are remarkable, even more so are the formations of the CPQP and the static UO.sub.2 DOS from their respective excitation impulses within the 40 femtosecond width of the measurement with no sign of the normal intermediate state. The optical switching time is therefore zero on this time scale, consistent with the different outcomes with the different excitation energies. The partly filled bands above the chokepoint that form with 3.1 eV excitation and span the entire range of energy (
(102) These results validate and extend our model for the CPQP and continue to highlight the preeminence of UO.sub.2 as a system encompassing many of the current ideas about dynamic electron-phonon coupling as the origin of the polaron physics of Mott insulators and the convergence of Bose-Einstein and BCS condensates. We also note the observation that the Fano-Feshbach resonance that is not universal in non-equilibrium BECs is associated with a change in chemical speciation, differentiating homogeneous non-equilibrium BECs where the quasiparticles are only perturbations of the ground state from heterogeneous ones that involve a chemical reaction and coherent exchange between the ground and excited state species. Additional novel properties may be found as this system is explored more thoroughly.
(103) Experimental Design.
(104) These experiments elucidate the response of the density of states around the Mott gap to O-doping by using U M RIXS to probe the occupied states below the Fermi level in UO.sub.2, U.sub.4O.sub.9, and U.sub.3O.sub.7, and O XAS and NIXS to probe the unoccupied states above the Fermi level in the same compounds. These measurements were complemented by similar ones on relevant standards, Cs.sub.2UO.sub.2Cl.sub.4, U.sub.3O.sub.8, and UO.sub.3, to be used to understand the assignments and trends. These were supplemented by O XAS measurements on UO.sub.2 and U.sub.4O.sub.9 samples mounted on the end of liquid nitrogen cooled cold finger to determine whether changing the temperature would affect the electron distribution even in the absence of a phase transition. Time resolved photoemission experiments coincident with the excitation pulse at a range of fluences with 1.6, 3.1, and 4.7 eV excitation energy were used to probe the response of the density of states around the Mott gap to photo-doping, which creates U(III) and U(V) polarons in UO.sub.2 without lattice defects. The experiments were supplemented by calculations of the densities of states to predict the changes that would be expected with O-doping and the x-ray measurements for comparison with the experimental results.
(105) Experimental Methods. The materials and experimental procedures and modeling methods have been described previously (18, 19, 37, 38, 87, 89, 90) in addition to the following information.
(106) The O K non-resonant inelastic x-ray scattering (NIXS) spectra of UO.sub.2 and U.sub.3O.sub.7 were measured at the same time as the O.sub.4, 5 NIXS spectra previously reported (37) and therefore were from the same materials and used the same preparation and experimental methods (121). The UO.sub.2, U.sub.3O.sub.7, and U.sub.4O.sub.9 for the NIXS measurement were from the same materials as those used for a combined neutron and x-ray pair distribution function and U L.sub.3 X-ray Absorption Fine Structure spectroscopy study (18). The single crystal of UO.sub.2 was from the same boule as used in previous ultrafast optical studies (122). The sample of Cs.sub.2UO.sub.2Cl.sub.4 was also from the same material used for in our O.sub.4, 5 NIXS report (37). The O K fluorescence yield (FY) XAS measurements were also performed as reported previously (121) except that the UO.sub.2+x/U.sub.4O.sub.9 spectra were measured on beamline 10-1 instead of 8-2. A synopsis of these procedures as well as descriptions of those not included in this list follows. For the time resolved photoemission (38), the number of excitations is calculated using the listed fluences, 1 nm thickness, optical densities of 1.210.sup.5 cm.sup.1 at 3.1 eV and 1.010.sup.5 cm.sup.1 at 4.7 eV (123), density of 11.0 g/cm.sup.3, and a formula weight for UO.sub.2 of 270 g. No scattering correction was made.
(107) Preparation of Samples. Ultrapure UO.sub.2 was prepared by precipitating UO.sub.2(O.sub.2) from aqueous solution, converted to UO.sub.3 by heating in air at 400 C., followed by reduction with H.sub.2 at 500 C. U.sub.4O.sub.9 for the NIXS measurement and U.sub.3O.sub.7 were made by heating a mixture of the appropriate amounts of U.sub.3O.sub.8 and UO.sub.2 in a sealed quartz tube at 1000 C. for 15 days. Amorphous UO.sub.3 was prepared by heating UO.sub.2(O.sub.2) at 400 C. in air for 6 hours. It is assumed that this is locally identical to UO.sub.3 (124) that results from heating at a somewhat higher temperature (125) and differs in the U vacancies being disordered. Orthorhombic U.sub.3O.sub.8 was prepared by heating UO.sub.2(O.sub.2) in air at 800 C. and verified by XRD. The FY samples of UO.sub.2.25/U.sub.4O.sub.9 were made from the controlled oxidation of a different UO.sub.2 starting material and verified by XAFS, XRD, and weight. Cs.sub.2UO.sub.2Cl.sub.4 was prepared by the previously reported methods (37). Purity was checked by XRD, and for the fluorite compounds by neutron scattering and U L.sub.3 XAFS, all of which were previously reported (18). All compounds were handled anaerobically because we have on some occasions observed relatively rapid changes in the U L.sub.3 and O K XAFS spectra of UO.sub.2 that imply oxidation on exposure to air, probably because of the condition of the surface. Samples were ground and cast into polystyrene films under inert atmosphere as reported (37, 121). Those for NIXS were around 70 wt-% of the material, 30 wt-% polystyrene. O K XAS samples were much more dilute, around 5 wt-%, and were mixed with C powder before casting into the polystyrene solutions poured into ca. 26 mm wells in individual Cu blocks, with 20 of C subsequently sputtered onto their surfaces for protection and conduction.
(108) Oxygen K-Edge NIXS and Fluorescence Yield Measurements.
(109) All NIXS measurements were taken using the lower energy resolution inelastic X-ray scattering (LERIX) user facility at the PNC/XOR 20-ID undulator beamline of the Advanced Photon Source (126) using a double-crystal Si (111) monochromator with incident photon flux of 10.sup.12/s. The net energy resolution (fwhm) of the monochromator and the LERIX analyzer crystals is 1.3 eV, as determined from the width of the elastic scattering line. An interval of 0.2 eV was used in the actual measurement, counting for 80 seconds at each point for a total time of 6-10 hours per spectrum. NIXS data extraction and processing followed methods reported previously (126, 127). The dipole approximation to the NIXS cross section was verified by the independence of the oxygen K-edge shape over the range of q reported, so that the spectra shown here are the summed counts from six different detectors spanning from q 3.3 to 4.8 a.u. The typical measurement time per data point is 80 s, which yields 5000 counts in the q-integrated edge step above the 60 000 counts from background due to the valence Compton scattering. Although the polystyrene matrix darkened in color during the measurement, the NIXS data were unaffected as determined by comparing spectra as the total dose accumulated.
(110) Room temperature O K-edge XAS data were recorded at the Stanford Synchrotron Radiation Lightsource (SSRL) at VUV beamline 8-2 (128), utilizing bending magnet radiation and a spherical grating monochromator, under synchrotron ring conditions of 3.0 GeV and 85-100 mA. A standard vacuum system was used, except that for U a 1200 carbon window was used to isolate the chamber from the upstream instrumentation and ring. The incident radiation was monitored using an Au grid with 80% transmission. The fluorescence was measured at normal incidence using two International Radiation Detector XUV100 type photodiodes coated with 1000 of aluminum to reduce visible light absorption. This was accomplished by placing the photodiodes facing the sample with a 3 mm gap between them for the passage of the beam. The diodes were 5-10 mm from the sample and were mounted in a cavity in a grounded copper block to prevent electrical interference. The total electron yield (TEY) and FY data for the spectra of the various compounds showed no sign of radiation damage. The UO.sub.2+x and U.sub.4O.sub.9 were measured on beamline 10-1, a wiggler source with a similar monochromator. The sample was turned 45 and the diode monitoring the fluorescence was located at a right angle relative to the beam direction in the horizontal plane. FY data were converted to absorbance by dividing the diode by a Au grid current, similar to the 8-2 experiment. For both the 8-2 and 10-1 experiment, the spectra were normalized by subtracting a line that was fitted through a flat region below the initial rise in absorbance and the spectra offset so that the extrapolated value of this line at 553 eV equaled zero, then multiplied by a factor so that the value of a second line fitted over the flat region above the absorption edge features (approximately 550-590 eV) was unity at this same value. In some spectra sloping backgrounds beyond the spectral peaks caused the absorption to be below one in this region, resulting in a diminution in the amplitudes of these peaks as well. However, since we only compare relative amplitudes within a spectrum this has no effect on the interpretation of the results. Curve-fits to identify spectral features were performed with Gaussians plus an arctangent function to approximate the transition to the continuum. This arctangent was positioned prior to optimization within the higher energy peak, consistent with the assignment for UO.sub.2Cl.sub.4.sup.2 (83) and with the analogous behavior of transition metal oxides.(129) Because this results in a difference with previous assignments of the spectral features to electronic states, instead of referring to the lower and higher energy peaks as 5f and 6d we use the nomenclature from higher energy core transition metal level spectroscopy and refer to them as, respectively, the pre-edge that should be transitions to bound states and the white line that may include transitions to bound states, the transition to the continuum that begins at the ionization energy, and transitions to quasi-bound states.
(111) U M5 RIXS Measurements.
(112) The RIXS experiment at the U M.sub.5 edge was performed at the ID26 beamline of the European Synchrotron Radiation Facility(130). The incident energy was selected using the (111) reflection from a cryo-cooled Si crystal monochromator. Rejection of higher harmonics was achieved by three Si mirrors at the angles of 3.5, 4.0 and 2.5 mrad respectively. The beam size of 0.10.4 mm (verticallyhorizontally) was measured. The valence to core RIXS at the U M.sub.5 edge was recorded by X-ray emission spectrometer (131, 132) equipped with five Si(220) crystal analyzers. The intensity was normalized to the incident flux.
(113) DFT/LDA+U Calculations
(114) DFT+U or LDA+U calculations (133) based on projector augmented wave (PAW) potentials (134, 135) were carried out for UO.sub.2 and the calculated structures for the U.sub.4O.sub.9 and U.sub.3O.sub.7 phases that are analogous to the neutron structures with large unit cells using the same computer code as the hybrid calculations (VASP) (136). These two phases were described with the structure models derived from ordering of quad-interstitial clusters (90), which correspond to the 0 K minimum energy configurations predicted by DFT+U (90). As reference, calculations were also performed on stoichiometric UO.sub.2 described with a 222 fluorite supercell. All DFT+U calculations applied plane wave cut-off energy of 500 eV. Both volume and internal structural parameters were relaxed for all crystal structures. The latter was relaxed until the Hellmann-Feynman forces on each ion were sufficiently small (<0.02 eV/A) or until the total energy was converged to at least 0.0001 eV/atom. For UO.sub.2 a 222 Monkhorst-Pack k point mesh was used and other structures applied meshes of approximately the same density. Convergence with respect to k points was verified for all cases. The Brillouin zone integration applied Gaussian smearing with a smearing parameter of 0.05 eV. The U and J parameters of, respectively, 4.5 and 0.5 eV, were taken from the UO.sub.2 values determined by Dudarev et al. (137) and issues related to meta-stable electronic solutions were addressed using the reported approaches (138, 139).
(115) FEFF9 Calculations.
(116) Calculations of O K-edge XANES and LDOS were carried out for UO.sub.2 and Cs.sub.2UO.sub.2Cl.sub.4 using a version of the FEFF9 self-consistent real-space multiple scattering code (140, 141), which was extended to include spin-orbit splitting in the calculation of the LDOS. Valence densities and potentials were calculated self-consistently, and the U f states were allowed to relax. The calculations of the spectra were converged with respect to both the cluster sizes used for the modeling of the systems, and the maximum angular momentum used in the full multiple scattering (FMS) calculations. Final state effects were included using a constant Lorentzian broadening to account for the finite lifetime of the core-hole, and the Hedin-Lundquist self-energy model to account for the interactions between the photo-electron and the valence system. Additional core-hole effects were included via the final state rule, and compared to calculations without core-hole interactions.
(117) Dirac-Hartree-Fock Calculations.
(118) Additional evaluations of the effects of ligand field splitting and of spin-orbit coupling on multiplet splitting in the spectrum of UO.sub.2 were obtained from relativistic Dirac-Hartree-Fock type calculations (87, 142) on the bare U.sup.4+ ion with only spin-orbit splitting and the UO.sub.8 cluster that will exhibit both spin-orbit and ligand field splitting. The bare U.sup.4+ cation is a simple atomic model for U(IV) in UO.sub.2 and neglects ligand field effects, including covalent mixing of U and O orbitals to form bonding and anti-bonding orbitals. The ligand field effects are taken into account with an embedded UO.sub.8 cluster (143), which includes, in particular, the covalent mixing of U and O frontier orbitals (144). Furthermore, in order to represent multiplet effects for the XAS excited states, we consider wavefunctions for configurations of U.sup.3+ where an additional electron is added to the frontier orbitals of U.sup.4+, as discussed below. The wave functions for the cluster were determined with the full four-component formalism (143), including spin-orbit splitting, and also with a spin-free Hamiltonian (145) where only the scalar relativistic terms are included but the spin-orbit splitting is neglected. All calculations reported for U.sup.4+, UO.sub.8, and U.sup.3+ were performed with the Dirac08 program system (146); details of the U.sup.4+ and UO.sub.8 embedded cluster calculations are given in (143). For U.sup.3+, the multiplet splittings were determined for two configurations with 4-component orbitals for these configurations optimized with Dirac-Hartree-Fock calculations for the average of configurations. The angular momentum coupling of the valence level electrons for the isolated U.sup.3+ cation, with open shell occupations of 5f.sup.3 and 5f.sup.26d.sup.1 that are the U configurations that could be generated from excitations from an O is shell, which is not explicitly taken into account in this atomic model, was introduced by configuration mfixing of determinants that have different distributions of the electrons over the 14 5f spinors and the 10 6d spinors. This configuration mixing takes full account of the intermediate angular momentum coupling of the open shell electrons between j-j coupling and Russell-Saunders LS coupling. The computational procedures were as described in Ref. (87).
(119) Statistical Analysis.
(120) Spectroscopic results such as these that do not utilize amplitudes quantitatively are not amenable to statistical analysis. Noise levels, and the associated significance of the results, can be estimated by inspection. Uncertainties in energy are typically 0.1-0.2 eV.
(121) Turning to
(122) Continuing to refer to
(123) Continuing to refer to
(124) Continuing to refer to
(125) In some embodiments, the UO.sub.2+x excitation source 112 is a metal such as aluminum, copper, silver, or gold. In some embodiments, the UO.sub.2+x excitation source 112 is less than 10 nM thick. In some embodiments, the UO.sub.2+x excitation source 112 is less than 5 nM thick.
(126) Continuing to refer to
(127) Continuing to refer to
(128) Electrical device 1602 is advantageous because the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 can be switched from the electrically conducting state to the electrically non-conductive state very quickly and thus serve as a very fast switching gate. Electrical device 1602 is further advantageous because of the electrical conductivity of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state. For instance, in some embodiments, the electrical conductivity of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state is at least one thousand times that of copper. In some embodiments, the electrical conductivity of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state is at least ten thousand times that of copper, one million times that of copper, or ten million times that of copper. Stated differently, in some embodiments, the electrical resistance of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state is at least one thousand times less than the resistance of copper. In some embodiments, the electrical resistance of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state is at least 10 thousand times less than the resistance of copper, one million times less than the resistance of copper, or 10 million times less than the resistance of copper. As such, the electrical device 1602 illustrated in
(129) As such, in some embodiments, the electrical device 1602 is a transmission line and what is depicted in
(130) Turning to
(131) Continuing to refer to
(132) Continuing to refer to
(133) In the electrical device 1704, the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 is operable between an electrically conducting state and an electrically non-conductive state. The first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film is in the electrically conducting state when at least a threshold current is run from the first lead 106 to the second lead 108 of device 1704 or there is greater than a first voltage differential between the first lead and the second lead. The first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 is in the electrically nonconducting state when less than the threshold current is run from the first lead 106 to the second lead 108 of the device 1604 or there is less than the first voltage differential between the first lead and the second lead.
(134) Electrical device 1604 is advantageous because the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 can be switched from the electrically conducting state to the electrically non-conductive state very quickly and thus act as a very fast switching gate. Electrical device 1604 is further advantageous because of the electrical conductivity of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state. For instance, in some embodiments, the electrical conductivity of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state is at least one thousand times that of copper. In some embodiments, the electrical conductivity of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state is at least 10 thousand times that of copper, one million times that of copper, or 10 million times that of copper. Stated differently, in some embodiments, the electrical resistance of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state is at least one thousand times less than the resistance of copper. In some embodiments, the electrical resistance of the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 when in the electrically conducting state is at least 10 thousand times less than the resistance of copper, one million times less than the resistance of copper, or 10 million times less than the resistance of copper. As such, the electrical device 1604 illustrated in
(135) As such, in some embodiments, the electrical device 1604 is transmission line and what is being visualized in
(136) Turning to
(137) Continuing to refer to
(138) Continuing to refer to
(139) Continuing to refer to
(140) In some embodiments the excitation source 120 is configured to polarize a region of the first single crystal or the first oriented crystal UO.sub.2+x film 102 to activate the non-equilibrium polaronic quantum phase-condensate and thereby determine an electrical conductivity of the first single crystal or the first oriented crystal UO.sub.2+x film 102. A first state of the excitation source 120 causes the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 to be electrically conducting. A second state of the excitation source 120 causes the first single UO.sub.2+x crystal or the first oriented crystal UO.sub.2+x film 102 to be electrically non-conductive. In some such embodiments, the first state of the excitation source 120 is characterized by a first alternating current that is run through the excitation source 120 (e.g., from the left to the right in the perspective of
(141)
(142) Continuing with
(143) Turning to
(144) Continuing to refer to
(145) Continuing to refer to
(146) Continuing to refer to
(147) In some embodiments, the UO.sub.2+x excitation source 112 is a metal such as aluminum, copper, silver, or gold. In some embodiments, the UO.sub.2+x excitation source 112 is less than 10 nM thick. In some embodiments, the UO.sub.2+x excitation source 112 is less than 5 nM thick.
(148) Continuing to refer to
(149) Continuing to refer to
(150) In some embodiments, one or more of the components of the devices illustrated in
(151) Chemical Vapor Deposition.
(152) In some embodiments, one or more layers of the disclosed electrical devices are deposited by chemical vapor deposition. In chemical vapor deposition (CVD), the constituents of a vapor phase, often diluted with an inert carrier gas, react at a hot surface (typically higher than 190 C.) to deposit a solid film. Generally, chemical vapor deposition reactions require the addition of energy to the system, such as heating the chamber or the wafer. For more information on chemical vapor deposition, exemplary devices used to perform chemical vapor deposition, and process conditions are used to perform chemical vapor deposition of silicon nitride, see Van Zant, Microchip Fabrication, Fourth Edition, McGraw-Hill, New York, 2000, pp. 363-393; and Madou, Fundamentals of Microfabrication, Second Edition, 2002, pp. 144-154, CRC Press, each of which are hereby incorporated by reference herein in their entireties.
(153) Reduced Pressure Chemical Vapor Deposition.
(154) In some embodiments, one or more layers of the disclosed electrical devices are deposited by reduced pressure chemical vapor deposition (RPCVD). RPCVD is typically performed at below 10 Pa and at temperatures in the range of (550 C.-600 C.). The low pressure used in RPCVD results in a large diffusion coefficient, which leads to growth of a layer that is limited by the rate of surface reactions rather than the rate of mass transfer to the substrate. In RPCVD, reactants can typically be used without dilution. RPCVD is performed, for example, in some embodiments, in a horizontal tube hot wall reactor.
(155) Low Pressure Chemical Vapor Deposition.
(156) In some embodiments, one or more layers of the disclosed electrical devices are deposited by low pressure chemical vapor deposition (LPCVD) or very low pressure CVD. LPCVD is typically performed at below 1 Pa.
(157) Atmospheric Chemical Vapor Deposition.
(158) In some embodiments, one or more layers of the disclosed electrical devices are deposited by atmospheric to slightly reduced pressure chemical vapor deposition. Atmospheric pressure to slightly reduced pressure CVD (APCVD) is used, for example, to grow APCVD is a relatively simplistic process that has the advantage of producing layers at high deposition rates and low temperatures (350 C.-400 C.).
(159) Plasma Enhanced Chemical Vapor Deposition.
(160) In some embodiments, one or more layers of the disclosed electrical devices are deposited by plasma enhanced (plasma assisted) chemical vapor deposition (PECVD). PECVD systems feature a parallel plate chamber operated at a low pressure (e.g., 2-5 Torr) and low temperature (300 C.-400 C.). A radio-frequency-induced glow discharge, or other plasma source is used to induce a plasma field in the deposition gas. PECVD systems that are used include, but are not limited to, horizontal vertical flow PECVD, barrel radiant-heated PECVD, and horizontal-tube PECVD. In some embodiments, remote plasma CVD (RPCVD) is used. Remote plasma CVD is described, for example, in U.S. Pat. No. 6,458,715 to Sano et al., which is hereby incorporated by reference in its entirety.
(161) Anodization.
(162) In some embodiments, one or more layers of the disclosed electrical devices are deposited by anodization. Anodization is an oxidation process performed in an electrolytic cell. The material to be anodized becomes the anode (+) while a noble metal is the cathode (). Depending on the solubility of the anodic reaction products, an insoluble layer (e.g., an oxide) results. If the primary oxidizing agent is water, the resulting oxides generally are porous, whereas organic electrolytes lead to very dense oxides providing excellent passivation. See, e.g., Madou et al., 1982, J. Electrochem. Soc. 129, pp. 2749-2752, which is hereby incorporated by reference in its entirety.
(163) Sol-Gel Deposition Techniques.
(164) In some embodiments, one or more layers of the disclosed electrical devices are deposited by a sol gel process. In a sol-gel process solid particles, chemical precursors, in a colloidal suspension in a liquid (a sol) forms a gelatinous network (a gel). Upon removal of the solvent by heating a glass or ceramic layer. Both sol and gel formation are low temperature processes. For sol formation, an appropriate chemical precursor is dissolved in a liquid, for example, tetraethylsiloxane (TEOS) in water. The sol is then brought to its gel-point, that is, the point in the phase diagram where the sol abruptly changes from a viscous liquid to a gelatinous, polymerized network. In the gel state the material is shaped (e.g., a fiber or a lens) or applied onto a substrate by spinning, dipping, or spraying. In the case of TEOS, a silica gel is formed by hydrolysis and condensation using hydrochloric acid as the catalyst. Drying and sintering at temperatures between 200 C. to 600 C. transforms the gel into a glass and ultimately into silicon dioxide.
(165) In the semiconductor industry the sol-gel method described is often used to deposit silicon dioxide. The method is known as the Spin-On Glass method (SOG). Spin-On Glass materials have been widely used as a diffusion source or a planarizing dielectric or multilevel metalization schemes in the fabrication of nowadays integrated circuits. SOGs are in general SiO network polymers in organic solvents, and prepared through the hydrolysis-condensation reaction that implied the sol-gel technology. SOG materials can be divided into three groups: 1) silicate based compounds, 2) organosilicon compounds and 3) dopant-organic compounds. More information on SOG can be found, for example, in Nguyen Nhu Toan, Spin-On Glass Materials and Applications in Advanced IC Technologies, 1999, which is hereby incorporated herein by reference in its entirety.
(166) Vacuum Evaporation.
(167) In one embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by vacuum evaporation. Vacuum evaporation takes place inside an evacuated chamber. The chamber can be, for example, a quartz bell jar or a stainless steel enclosure. Inside the chamber is a mechanism that evaporates the metal source, a wafer holder, a shutter, thickness and rate monitors, and heaters. The chamber is connected to a vacuum pump. There are any number of different ways in which the metal is evaporated within the chamber, including filament evaporation, E-beam gun evaporation, and hot plate evaporation. See, for example, Van Zant, Microchip Fabrication, Fourth Edition, McGraw-Hill, New York, 2000, pp. 407-411, which is hereby incorporated by reference herein in its entirety.
(168) Sputter Deposition/Physical Vapor Deposition.
(169) In another embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by sputtering. Sputtering, like evaporation, takes place in a vacuum. However, it is a physical not a chemical process (evaporation is a chemical process), and is referred to as physical vapor deposition. Inside the vacuum chamber is a slab, called a target, of the desired film material. The target is electrically grounded. An inert gas such as argon is introduced into the chamber and is ionized to a positive charge. The positively charged argon atoms are attracted to the grounded target and accelerate toward it.
(170) During the acceleration they gain momentum, and strike the target, causing target atoms to scatter. That is, the argon atoms knock off atoms and molecules from the target into the chamber. The sputtered atoms or molecules scatter in the chamber with some coming to rest on the wafer. A principal feature of a sputtering process is that the target material is deposited on the wafer with chemical or compositional change. In some embodiments of the present disclosure, direct current (DC) diode sputtering, radio frequency (RF) diode sputtering, triode sputtering, DC magnetron sputtering or RF magnetron sputtering is used. See, for example, Van Zant, Microchip Fabrication, Fourth Edition, McGraw-Hill, New York, 2000, pp. 411-415; U.S. Pat. Nos. 5,203,977; 5,486,277; and 5,742,471, each of which is hereby incorporated by reference herein in its entirety.
(171) RF diode sputtering is a vacuum coating process where an electrically isolated cathode is mounted in a chamber that can be evacuated and partially filled with an inert gas. If the cathode material is an electrical conductor, a direct-current high-voltage power supply is used to apply the high voltage potential. If the cathode is an electrical insulator, the polarity of the electrodes is reversed at very high frequencies to prevent the formation of a positive charge on the cathode that would stop the ion bombardment process. Since the electrode polarity is reversed at a radio frequency, this process is referred to as 133 sputtering. Magnetron sputtering is different form of sputtering. Magnetron sputtering uses a magnetic field to trap electrons in a region near the target surface thus creating a higher probability of ionizing a gas atom. The high density of ions created near the target surface causes material to be removed many times faster than in diode sputtering. The magnetron effect is created by an array of permanent magnets included within the cathode assembly that produce a magnetic field normal to the electric field.
(172) Collimated Sputtering.
(173) In another embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by collimated sputtering. Collimated sputtering is a sputtering process where the arrival of metal occurs at an angel normal to the wafer surface. The metal is collimated by a thick honeycomb grid that effectively blocks off angle metal atoms in some embodiments. Alternatively, ionizing the metal atoms and attracting them towards the wafer collimates the metal. Collimated sputtering improves filling of high aspect ratio contacts.
(174) Laser Ablated Deposition.
(175) In another embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by laser ablated deposition. In one form of laser ablated deposition, a rotating cylindrical target surface is provided for the laser ablation process. The target is mounted in a vacuum chamber so that it is rotated about the longitudinal axis of the cylindrical surface target and simultaneously translated along the longitudinal axis. A laser beam is focused by a cylindrical lens onto the target surface along a line that is at an angle with respect to the longitudinal axis to spread a plume of ablated material over a radial arc. The plume is spread in the longitudinal direction by providing a concave or convex lateral target surface. The angle of incidence of the focused laser beam is other than normal to the target surface to provide a glancing geometry in some embodiments. Simultaneous rotation about and translation along the longitudinal axis produce a smooth and even ablation of the entire cylindrical target surface and a steady evaporation plume. Maintaining a smooth target surface is useful in reducing undesirable splashing of particulates during the laser ablation process and thereby depositing high quality thin films. See, for example, U.S. Pat. No. 5,049,405, which is hereby incorporated by reference herein in its entirety.
(176) Molecular Beam Deposition.
(177) In another embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by molecular beam deposition. Molecular beam deposition is a method of growing films, under vacuum conditions, by directing one or more molecular beams at a substrate. In some instances, molecular beam deposition involves epitaxial film growth on single crystal substrates by a process that typically involves either the reaction of one or more molecular beams with the substrate or the deposition on the substrate of the beam particles. The term molecular beam refers to beams of monoatomic species as well as polyatomic species. The term molecular beam deposition includes both epitaxial growth and nonepitaxial growth processes. Molecular beam deposition is a variation of simple vacuum evaporation. However, molecular beam deposition offers better control over the species incident on the substrate than does vacuum evaporation. Good control over the incident species, coupled with the slow growth rates that are possible, permits the growth of thin layers having compositions (including dopant concentrations) that are precisely defined. Compositional control is aided by the fact that growth is generally at relatively low substrate temperatures, as compared to other growth techniques such as liquid phase epitaxy or chemical vapor deposition, and diffusion processes are very slow.
(178) Essentially arbitrary layer compositions and doping profiles are obtained with precisely controlled layer thickness. In fact, layers as thin as a monolayer are grown by MBE. Furthermore, the relatively low growth temperature permits growth of materials and use of substrate materials that could not be used with higher temperature growth techniques. See for example, U.S. Pat. No. 4,681,773, which is hereby incorporated by reference herein in its entirety.
(179) Ionized Physical Vapor Deposition.
(180) In another embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by ionized physical vapor deposition (I-PVD), also known as ionized metal plasma (IMP). In I-PVD, metal atoms are ionized in an intense plasma. Once ionized, the metal is directed by electric fields perpendicular to the wafer surface. Metal atoms are introduced into the plasma by sputtering from the target. A high density plasma is generated in the central volume of the reactor by an inductively coupled plasma (ICP) source. This electron density is sufficient to ionize approximately 80% of the metal atoms incident at the wafer surface. The ions from the plasma are accelerated and collimated at the surface of the wafer by a plasma sheath. The sheath is a region of intense electric field that is directed toward the wafer surface. The field strength is controlled by applying a radio frequency bias.
(181) Ion Beam Deposition.
(182) In another embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by ion beam deposition (IBD). IBD uses an energetic, broad beam ion source carefully focused on a grounded metallic or dielectric sputtering target. Material sputtered from the target deposits on a nearby substrate to create a film. Most applications also use a second ion source, termed an ion assist source (IAD), which is directed at the substrate to deliver energetic noble or reactive ions at the surface of the growing film. The ion sources are gridded ion sources and are typically neutralized with an independent electron source. IBD processing yields excellent control and repeatability of film thickness and properties. Process pressures in IBD systems are approximately 10-4 Torr. Hence, there is very little scattering of either ions delivered by the ion sources or material sputtered from the target of the surface. Compared to sputter deposition using magnetron or diode systems, sputter deposition by IBD is highly directional and more energetic. In combination with a substrate fixture that rotates and changes angle, IBD systems deliver a broad range of control over sidewall coatings, trench filling and liftoff profiles.
(183) Atomic Layer Deposition.
(184) In another embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by atomic layer deposition. Atomic layer deposition is also known as atomic layer epitaxy, sequential layer deposition, and pulsed-gas chemical vapor deposition. Atomic layer deposition involves use of a precursor based on self-limiting surface reactions. Generally, an object is exposed to a first species that deposits as a monolayer on the object. Then, the monolayer is exposed to a second species to form a fully reacted layer plus gaseous byproducts. The process is typically repeated until a desired thickness is achieved. Atomic layer deposition and various methods to carry out the same are described in U.S. Pat. No. 4,058,430 to Suntola et al., entitled Method for Producing Compound Thin Films, U.S. Pat. No. 4,413,022 to Suntola et al., entitled Method for Performing Growth of Compound Thin Films, to Ylilammi, and George et al., 1996, J. Phys. Chem. 100, pp. 13121-13131, each of which is hereby incorporated by reference herein in its entirety. Atomic layer deposition has also been described as a chemical vapor deposition operation performed under controlled conditions that cause the deposition to be self-limiting to yield deposition of, at most, a monolayer. The deposition of a monolayer provides precise control of film thickness and improved compound material layer uniformity. Atomic layer deposition is performed using equipment such as the Endura Integrated Cu Barrier/Seed system (Applied Materials, Santa Clara, Calif.).
(185) Hot Filament Chemical Vapor Deposition.
(186) In another embodiment of the present disclosure, one or more layers of the disclosed electrical devices are deposited by hot filament chemical vapor deposition (HFCVD). In HFCVD, reactant gases are flowed over a heated filament to form precursor species that subsequently impinge on the substrate surface, resulting in the deposition of high quality films. HFCVD has been used to grow a wide variety of films, including diamond, boron nitride, aluminum nitride, titanium nitride, boron carbide, as well as amorphous silicon nitride. See, for example, Deshpande et al., 1995, J. Appl. Phys. 77, pp. 6534-6541, which is hereby incorporated by reference herein in its entirety.
REFERENCES CITED
(187) All references cited herein, including those set forth in the List of References section below, are hereby incorporated by reference in their entirety and for all purposes to the same extent as if each individual publication or patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety for all purposes.
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Alternative Embodiments
(189) Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.