Isotope effect in superconducting lanthanum hydride under high compression

TL;DR

This study uses first-principles calculations to confirm that the isotope effect in LaH10 under high pressure aligns with conventional electron-phonon coupling theory, supporting phonons' role in its room-temperature superconductivity.

Contribution

It provides a theoretical validation of the isotope effect in LaH10, confirming the conventional phonon-mediated mechanism for its high-temperature superconductivity.

Findings

The electron-phonon coupling constants decrease with pressure.

The isotope effect exponent is approximately 0.465, matching experimental results.

The isotope effect follows a M^{-α} dependence, supporting phonon-mediated superconductivity.

Abstract

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$_{10}$.