Microscopic mechanism of room-temperature superconductivity in compressed LaH10

Room-temperature 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 T-c up to similar 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 (E-F), thereby producing a van Hove singularity (vHs). The crystalline symmetry and the band topology around the high-symmetry points near E-F are thus demonstrated to be important for room-temperature 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 T-c. Our findings elucidate the microscopic mechanism of the observed high-T-c BCS-type superconductivity in LaH10, which can be generic to another recently observed high-T-c hydride H3S.