Effect of hydrogen content on superconductivity in La–H compounds

Abstract

Finding room-temperature superconductors is one of the most important subjects in scientific search. Due to its hydrogen clathrate structures, LaH10 has become one of the widely known room-temperature superconductors under pressure. So exploring the role of hydrogen content would help understanding the mechanism of superconductivity in the hydrides. Here, we explore the evolution of hydrogen content in lanthanum hydrides based on the first-principles calculations. We found new lanthanum hydrides at pressures, such as Cmcm-LaH. The electronic properties and electron–phonon coupling have been studied and found that Fm3¯m-LaH obtained an unexpected low Tc of ∼ 0.001 K. The superconductive mechanism has been studied in LaHx (x = 0, 1, 2, 3, 8, 10), where LaH0 means elemental lanthanum. We found that low content of hydrogen depresses the electron–phonon interaction in La–H compounds before H–H bonds formed. But with the increases of H content, the strong electron–phonon coupling of H atoms would help the compounds obtain high Tc. This result would explain the lanthanum hydrides with lower H content obtain weaker electron–phonon coupling and could not became potential high-temperature superconductors.