Microscopic mechanism of roomerature superconductivity in compressed LaH10

Roomerature superconductivity has been one of the most challenging subjects in modern physics. Recent experiments reported that lanthanum hydride LaH10±x (x<1) raises a superconducting transition temperature Tc up to ∼260 (or 250) K at high pressures around 190 (170) GPa. Here, based on first-principles calculations, we reveal that compressed LaH10 has symmetry-protected Dirac-nodal-line states, which split into holelike and electronlike bands at the high-symmetry points near the Fermi energy (EF), thereby producing a van Hove singularity (vHs). The crystalline symmetry and the band topology around the high-symmetry points near EF are thus demonstrated to be important for roomerature superconductivity. Further, we identify that the electronic states at the vHs are composed of strongly hybridized La f and H s orbitals, giving rise to a peculiar characteristic of electrical charges with anionic La and both anionic and cationic H species. Consequently, 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 LaH10, therefore yielding a high Tc. Our findings elucidate the microscopic mechanism of the observed high-Tc BCS-type superconductivity in LaH10, which can be generic to another recently observed high-Tc hydride H3S.