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 T-c 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 LaH(10 )and LaD10 decrease monotonously with increasing pressure and (ii) the isotope effect of T-c is nearly proportional to M-alpha (M: ionic mass) with alpha approximate to 0.465, irrespective of pressure. The predicted value of alpha agrees well with the experimental one (alpha = 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.