Isotope effect in superconducting lanthanum hydride under high compression

Abstract

Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of LaH10 under megabar pressure. Specifically, the isotope effect of Tc was measured by the replacement of hydrogen (H) with deuterium (D), demonstrating a driving role of phonons in the observed room-temperature SC. Herein, based on the first-principles calculations within the harmonic approximation, we reveal that (i) the identical electron-phonon coupling constants of fcc LaH10 and LaD10 decrease monotonously with increasing pressure and (ii) the isotope effect of Tc is nearly proportional to M-α (M: Ionic mass) with α≈ 0.465, irrespective of pressure. The predicted value of α agrees well with the experimental one (α=0.46) measured at around 150 GPa. Thus, our findings provide a theoretical confirmation of the conventional electron-phonon coupling mechanism in a recently discovered room-temperature superconductor of compressed LaH10.