Stability and bonding nature of clathrate H cages in a near-room-temperature superconductor LaH10 (original) (raw)
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“Tubular” Lanthanum Hydride: A New Class of High-Temperature Superconducting Materials
JETP Letters, 2019
Quantum calculations within density functional theory have predicted a new structure of lanthanum hydride La 2 H 24 that is dynamically stable up to pressures about 150 GPa. It is a semimetal and has a low symmetry of crystal lattice. An important feature of this structure is the existence of quasimolecular hydrogen chains, which leads to the presence of phonon frequencies of about 420 meV, exceeding the maximum vibration frequency of the metallic hydrogen Fddd phase (ω ~ 360 meV). These properties make it possible to expect a high superconducting transition temperature for lanthanum hydride La 2 H 24 .
Physical review research, 2022
Hydrogen-rich superhydrides are believed to be very promising high critical temperature (high T c) superconductors, with experimentally observed critical temperatures near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g., LaH 10 at 170 GPa and CeH 9 at 150 GPa. With the motivation of discovering new hydrogen-rich high T c superconductors at the lowest possible pressure, quantitative theoretical predictions are needed. In these promising compounds, superconductivity is mediated by the highly energetic lattice vibrations associated with hydrogen and their interplay with the electronic structure, requiring fine descriptions of the electronic properties, notoriously challenging for correlated f systems. In this paper, we propose a first-principles calculation platform with the inclusion of many-body corrections to evaluate the detailed physical properties of the Ce-H system and to understand the structure, stability, and superconductivity of CeH 9 at high pressure. We report how the calculation of T c is affected by the hierarchy of many-body corrections and obtain a compelling increase in T c at the highest level of theory, which goes in the direction of experimental observations. Our findings shed significant light on the search for superhydrides in close similarity with atomic hydrogen within a feasible pressure range. We provide a practical platform to further investigate and understand conventional superconductivity in hydrogen-rich superhydrides.
Superconductivity at 253 K in lanthanum–yttrium ternary hydrides
Materials Today, 2021
Here we report the high-pressure synthesis of a series of lanthanum-yttrium ternary hydrides obtained at pressures of 170-196 GPa via the laser heating of P6 3 /mmc LaY alloys with ammonia borane. As a result, we discovered several novel compounds: cubic hexahydride (La,Y)H 6 and decahydrides (La,Y) H 10 with a maximum critical temperature T C $ 253 K and an extrapolated upper critical magnetic field B C2 (0) of up to 135 T at 183 GPa. The current-voltage measurements show that the critical current density J C in (La,Y)H 10 is 12-27.7 kA/mm 2 at 4.2 K, which is comparable with that of commercial superconducting wires such as NbTi and Nb 3 Sn. (La,Y)H 6 and (La,Y)H 10 are among the first examples of ternary high-T C superconducting hydrides. Our experiments show that part of metal atoms in the structures of recently discovered Im3m-YH 6 and Fm3m-LaH 10 can be replaced with lanthanum ($70%) and yttrium ($25%), respectively, with the formation of unique ternary superhydrides containing metal-encapsulated cages La@H 24 and Y@H 32 , which are specific for Im3m-LaH 6 and Fm3m-YH 10. This work demonstrates that hydrides, unstable in pure form such as LaH 6 and YH 10 , may nevertheless be stabilized at relatively low pressures in solid solutions with superhydrides having the desired structure.
2021
Hydrogen-rich superhydrides are believed to be very promising high-Tc superconductors, with experimentally observed critical temperatures near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g. LaH10 at 170 GPa and CeH9 at 150 GPa. With the motivation of discovering new hydrogen-rich high-Tc superconductors at lowest possible pressure, quantitative theoretical predictions are needed. In these promising compounds, superconductivity is mediated by the highly energetic lattice vibrations associated with hydrogen and their interplay with the electronic structure, requiring fine descriptions of the electronic properties, notoriously challenging for correlated f systems. In this work, we propose a first-principles calculation platform with the inclusion of many-body corrections to evaluate the detailed physical properties of the Ce-H system and to understand the structure, stability and superconductivity of CeH9 at high pressure. We rep...
Isotope effect in superconducting lanthanum hydride under high compression
Physical Review B, 2020
Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of LaH10 under megabar pressure. Specifically, the isotope effect of Tc was measured by the replacement of hydrogen (H) with deuterium (D), demonstrating a driving role of phonons in the observed room-temperature SC. Herein, based on the first-principles calculations within the harmonic approximation, we reveal that (i) the identical electron-phonon coupling constants of fcc LaH10 and LaD10 decrease monotonously with increasing pressure and (ii) the isotope effect of Tc is nearly proportional to M −α (M : ionic mass) with α ≈ 0.465, irrespective of pressure. The predicted value of α agrees well with the experimental one (α = 0.46) measured at around 150 GPa. Thus, our findings provide a theoretical confirmation of the conventional electron-phonon coupling mechanism in a newly discovered room-temperature superconductor of compressed LaH10.
Journal of Superconductivity and Novel Magnetism
The uniquely characteristic macrostructures of binary hydrogen-clathrate compounds MH n formed at high pressure, a cage of hydrogens surrounding a central-atom host, is theoretically predicted in various studies to include structurally stable phonon-mediated superconductors. High superconductive transition temperatures T C have thus far been measured for syntheses with M = La, Y, and Th. In compressed LaH 10 , independent studies report T C of 250 K and over 260 K, a maximum in T C with pressure P, and normal-state resistance scaling with temperature (suggesting unconventional pairing). According to reported band structure calculations of Fm m-phase LaH 10 , the La is anionic, with the chemical valence electrons appearing evenly split between La and H 10. Thus, compressed LaH 10 contains the combination of structure, charge separation and optimal balanced allocation of valence electrons for supporting unconventional high-T C superconductivity mediated by Coulomb interactions between electronic charges associated with La and H 10. A general expression for the optimal superconducting transition temperature for MH n clathrates is derived as T C0 = k B 1 [(n + v)/2A] 1/2 e 2 /ζ, where is a universal constant, (n + v) is the chemical valence sum per formula unit, taking unity for H and v for atom M, A is the surface area of the H-polyhedron cage, and is the mean distance between the M site and the centroids of the polyhedron faces. Applied to Fm m LaH 10 , T C0 values of 249.8(1.3) K and 260.7(2.0) K are found for the two experiments. Associated attributes of charge allocation, structure, effective Coulomb potential, and H-D isotope effect in T C of Fm m LaH 10 and Im m H 3 S are discussed, along with a generalized prospective for Coulomb-mediated superconductivity in MH n .
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 .
Superconductivity of lithium-doped hydrogen under high pressure
Acta crystallographica. Section C, Structural chemistry, 2014
The high-pressure lattice dynamics and superconductivity of newly proposed lithium hydrides (LiH2, LiH6 and LiH8) have been extensively studied using density functional theory. The application of the Allen-Dynes modified McMillan equation and electron-phonon coupling calculations show that LiH6 and LiH8 are superconductors with critical temperatures (T(c)) of 38 K at 150 GPa for LiH6 and 31 K at 100 GPa for LiH8, while LiH2 is not a superconductor. The T(c) of LiH6 increases rapidly with pressure and reaches 82 K at 300 GPa due to enhancement of the electron-phonon coupling and the increased density of states at the Fermi level, while the T(c) of LiH8 remains almost constant.
Applied Sciences, 2022
Lanthanide hydrogen-rich materials have long been considered as one of the candidates with high-temperature superconducting properties in condensed matter physics, and have been a popular topic of research. Attempts to investigate the effects of different compositions of lanthanide hydrogen-rich materials are ongoing, with predictions and experimental studies in recent years showing that substances such as LaH10, CeH9, and LaH16 exhibit extremely high superconducting temperatures between 150–250 GPa. In particular, researchers have noted that, in those materials, a rise in the f orbit character at the Fermi level combined with the presence of hydrogen vibration modes at the same low energy scale will lead to an increase in the superconducting transition temperature. Here, we further elaborate on the effect of the ratios of lanthanide to hydrogen in these substances with the aim of bringing more clarity to the study of superhydrides in these extreme cases by comparing a variety of la...