Origin of High-Temperature Superconductivity in Compressed LaH${}_{10}$

Abstract

Room-temperature superconductivity has been one of the most challenging subjects in modern physics. Recent experiments reported that lanthanum hydride LaH${}_{10\pm x}$ ($x$$<$1) raises a superconducting transition temperature $T_{\mathrm{c}}$ up to $\sim$260 (or 215) K at high pressures around 190 (150) GPa. Here, based on first-principles calculations, we reveal the existence of topological Dirac-nodal-line (DNL) states in compressed LaH${}_{10}$. Remarkably, the DNLs protected by the combined inversion and time-reversal symmetry and the rotation symmetry create a van Hove singularity (vHs) near the Fermi energy, giving rise to large electronic density of states. Contrasting with other La hydrides containing cationic La and anionic H atoms, LaH${}_{10}$ shows a peculiar characteristic of electrical charges with anionic La and both cationic and anionic H species, caused by a strong hybridization of the La $f$ and H $s$ orbitals. We find that a large number of electronic states at the vHs are strongly coupled to the H-derived high-frequency phonon modes that are induced via the unusual, intricate bonding network of LaH${}_{10}$, thereby yielding a high $T_{\mathrm{c}}$. Our findings not only elucidate the microscopic origin of the observed high-$T_{\mathrm{c}}$ BCS-type superconductivity in LaH${}_{10}$, but also pave the route for achieving room-temperature topological superconductors in compressed hydrogen-rich compounds.

9 pages, 11 figures