Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of LaH$_{ 10}$ under megabar pressure. Specifically, the isotope effect of $T_{ \rm c}$ 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 LaD$_{ 10}$ decrease monotonously with increasing pressure and (ii) the isotope effect of $T_{ \rm c}$ is nearly proportional to $M^{ -{ \alpha}}$ ($M$: ionic mass) with ${ \alpha}$ ${ \approx}$ 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 newly discovered room-temperature superconductor of compressed LaH$_{ 10}$.
Categories: cond-mat.supr-con