High-$T$${}_{\text{C}}$ Superconductivity in Hydrogen Clathrates Mediated by Coulomb Interactions between Hydrogen and Central-Atom Electrons

Abstract

The uniquely characteristic macrostructures of binary hydrogen-clathrate compounds $M$H${}_{\text{n}}$ 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$${}_{\text{C}}$ have thus far been measured for syntheses with $M$ = La, Y, and Th. In compressed LaH${}_{\text{10}}$, independent studies report $T$${}_{\text{C}}$ of 250 K and over 260 K, a maximum in $T$${}_{\text{C}}$ with pressure $P$, and normal-state resistance scaling with temperature (suggesting unconventional pairing). According to reported band structure calculations of $Fm$$\bar{3}$$m$-phase LaH${}_{\text{10}}$, the La is anionic, with the chemical valence electrons appearing evenly split between La and H${}_{\text{10}}$. Thus, compressed LaH${}_{\text{10}}$ contains the combination of structure, charge separation, and optimal balanced allocation of valence electrons for supporting unconventional high-$T$${}_{\text{C}}$ superconductivity mediated by Coulomb interactions between electronic charges associated with La and H${}_{\text{10}}$. A general expression for the optimal superconducting transition temperature for $M$H${}_{\text{n}}$ clathrates is derived as $T$${}_{\text{C0}}$ = $k$${}_{\text{B}}$${}^{-1}$$\Lambda$[(n + $v$)/2$A$]${}^{1/2}$$e$${}^2$/$\zeta$, where $\Lambda$ 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 $\zeta$ is the mean distance between the $M$ site and the centroids of the polyhedron faces. Applied to $Fm$$\bar{3}$$m$ LaH${}_{\text{10}}$, $T$${}_{\text{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, . . .

25 pages, 9 figures, 3 tables

References in corpus (18)

• Superconductive "sodalite"-like clathrate calcium hydride at high pressures
• Cubic H${}_3$S around 200 GPa: an atomic hydrogen superconductor stabilized by sulfur
• Superconductivity in sodalite-like yttrium hydride clathrates
• Superconducting Phase-Diagram of H3S under High Magnetic Fields
• Superconductivity up to 243 K in yttrium hydrides under high pressure
• The road to room-temperature conventional superconductivity
• Fermi-Bose mixtures and BCS-BEC crossover in high-Tc superconductors
• Theory of High-Tc Superconductivity: Accurate Predictions of Tc
• Road to Room-Temperature Superconductivity: Tc above 260 K in Lanthanum Superhydride under Pressure
• Comment on "Superconductivity in electron-doped layered TiNCl with variable interlayer coupling"
• On the isotope effect in compressed superconducting H${}_{\text{3}}$S and D${}_{\text{3}}$S
• Superconducting interaction charge in thallium-based high-Tc cuprates: Roles of cation oxidation state and electronegativity
• Charge compensation and optimal stoichiometry in superconducting (Ca${}_x$La${}_{1-x}$)(Ba${}_{1.75-x}$La${}_{0.25+x}$)Cu${}_3$O${}_y$
• Spectroscopic signatures of phonons in high pressure superconducting hydrides
• Reply to "Comment on 'Isotope effect in high-Tc superconductors' "
• High-$T_{\text{C}}$ superconductivity in Cs${}_3$C${}_{60}$ compounds governed by local Cs-C${}_{60}$ Coulomb interactions
• Comment on "Isotope effect in high-Tc superconductors" (D. R. Harshman, J. D. Dow, and A. T. Fiory, Physical Review B v.77, 024523 (2008))
• Comparative study of high-Tc superconductivity in H3S and H3P

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