Abstract
Room-temperature superconductivity has been one of the most challenging subjects in modern physics. Recent experiments reported that lanthanum hydride () raises a superconducting transition temperature up to (or 250) K at high pressures around 190 (170) GPa. Here, based on first-principles calculations, we reveal that compressed has symmetry-protected Dirac-nodal-line states, which split into holelike and electronlike bands at the high-symmetry points near the Fermi energy (), thereby producing a van Hove singularity (vHs). The crystalline symmetry and the band topology around the high-symmetry points near 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 and H 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 , therefore yielding a high . Our findings elucidate the microscopic mechanism of the observed high- BCS-type superconductivity in , which can be generic to another recently observed high- hydride .
- Received 11 November 2018
- Revised 22 March 2019
DOI:https://doi.org/10.1103/PhysRevB.99.140501
©2019 American Physical Society