Superconductivity in FeH 5 (original) (raw)
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arXiv (Cornell University), 2021
Recently, YH 6 was synthesized as a first compound from theoretically predicted stable compressed MH 6 hydrides with bcc Im-3m crystal structures. Superconductivity of pressurized YH 6 was confirmed with critical temperature (T c) that is considerably lower than the predicted value by Migdal-Eliashberg (ME) theory. Here, we present theoretical reinvestigation of the superconductivity for selected MH 6 hydrides. Our results confirm that YH 6 and ScH 6 with Im-3m structure at corresponding GPa pressures are superconductors but with an anti-adiabatic character of superconducting ground state and a multiple-gap structure in one-particle spectrum. Transition into superconducting state is driven by strong electron-phonon coupling with phonons of H atom vibrations. Based on anti-adiabatic theory, calculated critical temperature T c in YH 6 is ≈ 231 K, i.e. just by ≈7 K higher than the experimental value. For ScH 6 the calculated critical temperature is T c ≈ 196 K. This value is by 27 K higher than a former theoretical prediction. Unexpected results concern CaH 6 and MgH 6 in Im-3m structure at corresponding GPa pressures. Calculated band structures (BS) indicate that in CaH 6 and MgH 6 the couplings to H stretching vibrations do not induce transitions into superconducting anti-adiabatic state and these hydrides remain stable in adiabatic metal-like state, which contradicts to former predictions of ME theory. These discrepancies are discussed in association with BS structure and a possible role of dorbitals on the involved metals, while we stress that the anti-adiabatic theory uses BS topology and its stability as a key input.
Physical review letters, 2009
Metallization in pure hydrogen has been proposed to give rise to high-temperature superconductivity at pressures which still lie beyond the reach of contemporary experimental techniques. Hydrogen-dense materials offer an opportunity to study related phenomena at experimentally achievable pressures. Here we report the prediction of high-temperature superconductivity in yttrium hydride (YH 3 ), with a T c of 40 K at 17.7 GPa, the lowest reported pressure for hydrogen-dense materials to date. Specifically, we find that the face-centered cubic structure of YH 3 exhibits superconductivity of different origins in two pressure regions. The evolution of T c with pressure follows the corresponding change of s-d hybridization between H and Y, due to an enhancement of the electron-phonon coupling by a matching of the energy level from Y-H vibrations with the peak of the s electrons from the octahedrally coordinated hydrogen atoms.
Journal of Applied Physics, 2021
Recently, YH 6 was synthesized as a first compound from theoretically predicted stable compressed MH 6 hydrides with bcc Im-3m crystal structures. Superconductivity of pressurized YH 6 was confirmed with critical temperature (T c) that is considerably lower than the predicted value by Migdal-Eliashberg (ME) theory. Here, we present theoretical reinvestigation of the superconductivity for selected MH 6 hydrides. Our results confirm that YH 6 and ScH 6 with Im-3m structure at corresponding GPa pressures are superconductors but with an anti-adiabatic character of superconducting ground state and a multiple-gap structure in one-particle spectrum. Transition into superconducting state is driven by strong electron-phonon coupling with phonons of H atom vibrations. Based on anti-adiabatic theory, calculated critical temperature T c in YH 6 is ≈ 231 K, i.e. just by ≈7 K higher than the experimental value. For ScH 6 the calculated critical temperature is T c ≈ 196 K. This value is by 27 K higher than a former theoretical prediction. Unexpected results concern CaH 6 and MgH 6 in Im-3m structure at corresponding GPa pressures. Calculated band structures (BS) indicate that in CaH 6 and MgH 6 the couplings to H stretching vibrations do not induce transitions into superconducting anti-adiabatic state and these hydrides remain stable in adiabatic metal-like state, which contradicts to former predictions of ME theory. These discrepancies are discussed in association with BS structure and a possible role of dorbitals on the involved metals, while we stress that the anti-adiabatic theory uses BS topology and its stability as a key input.
Electron-phonon interaction and superconductivity in metallic hydrogen
Ferroelectrics, 1977
A detailed study of the electron-phonon interaction in the Cmca phase of metallic hydrogen and of its implications in the superconducting properties is presented. A careful analysis of the role played by anisotropy and by the presence of superconducting multigaps allows to single out the peculiarities that drive superconductivity at very high temperature in this system.
Hydrogen-Induced High-Temperature Superconductivity in Two-Dimensional Materials: The Example of Hydrogenated Monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline">mml:mrowmml:msubmml:mrowmml:miMgBmml:mrowmml:mn2</m...
Physical Review Letters, 2019
Hydrogen-based compounds under ultra-high pressure, such as the polyhydrides H3S and LaH10, superconduct through the conventional electron-phonon coupling mechanism to attain the record critical temperatures known to date. We demonstrate here that the intrinsic advantages of hydrogen for phonon-mediated superconductivity can be exploited in a completely different system, namely two-dimensional (2D) materials. We find that hydrogen adatoms can strongly enhance superconductivity in 2D materials due to flatband states originating from atomic-like hydrogen orbitals, with a resulting high density of states, and due to the emergence of high-frequency hydrogen-related phonon modes that boost the electron-phonon coupling. As a concrete example, we investigate the effect of hydrogen adatoms on the superconducting properties of monolayer MgB2, by solving the fully anisotropic Eliashberg equations, in conjunction with a first-principles description of the electronic and vibrational states, and the coupling between them. We show that hydrogenation leads to a high critical temperature of 67 K, which can be boosted to over 100 K by biaxial tensile strain.
Superconductivity at 100 K in dense SiH4(H2)2 predicted by first principles
Proceedings of the National Academy of Sciences, 2010
Motivated by the potential high-temperature superconductivity in hydrogen-rich materials, the high-pressure structures of SiH 4 ðH 2 Þ 2 in the pressure range 50-300 GPa were extensively explored by using a genetic algorithm. An intriguing layered orthorhombic (Ccca) structure was revealed to be energetically stable above 248 GPa with the inclusion of zero-point energy. The Ccca structure is metallic and composed of hydrogen shared SiH 8 dodecahedra layers intercalated by orientationally ordered molecular H 2 . Application of the Allen-Dynes modified McMillan equation yields remarkably high superconducting temperatures of 98-107 K at 250 GPa, among the highest values reported so far for phononmediated superconductors. Analysis reveals a unique superconducting mechanism that the direct interactions between H 2 and SiH 4 molecules at high pressure play the major role in the high superconductivity, while the contribution from H 2 vibrons is minor.
Multiband nature of room-temperature superconductivity in LaH10 at high pressure
Physical Review B, 2020
Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of LaH 10 under megabar pressures. This SC of compressed LaH 10 has been explained in terms of strong electron-phonon coupling (EPC), but the mechanism of how the large EPC constant and high superconducting transition temperature T c are attained has not yet been clearly identified. Based on the density-functional theory and the Migdal-Eliashberg formalism, we reveal the presence of two nodeless, anisotropic superconducting gaps on the Fermi surface (FS). Here, the small gap is mostly associated with the hybridized states of H s and La f orbitals on the three outer FS sheets, while the large gap arises mainly from the hybridized state of neighboring H s or p orbitals on the one inner FS sheet. Further, we find that the EPC constant of compressed YH 10 with the same sodalite-like clathrate structure is enhanced due to the two additional FS sheets, leading to a higher T c than LaH 10. It is thus demonstrated that the multiband pairing of hybridized electronic states is responsible for the large EPC constant and room-temperature SC in compressed hydrides LaH 10 and YH 10 .
Physical review, 2021
We investigate the role of specific phonon mode symmetries for the room-temperature superconductivity in atomic hydrogen under large pressure. Using anisotropic Migdal-Eliashberg theory with ab initio input from density functional theory, we show that the E u phonon modes are the dominant driving force for obtaining such high critical temperatures. When going from 400 to 600 GPa, we find an increased transition temperature; however, the total electron-phonon coupling strength is counterintuitively reduced. Our analysis reveals that this is due to an enhanced contribution to the coupling strength by the E u phonon mode. We furthermore compute the momentum anisotropy of the superconducting gap which we find to be relatively small, about 7% of the mean gap value at 100 K.