Nonadiabatic and anharmonic effects in high-pressure H3S and D3S superconductors

TL;DR

This study uses advanced first-principles calculations to analyze how anharmonic and nonadiabatic effects influence superconductivity in high-pressure H3S and D3S, aligning theoretical Tc with experimental data.

Contribution

It explicitly incorporates anharmonic lattice dynamics and vertex corrections into the Eliashberg formalism, going beyond the Migdal approximation for more accurate predictions.

Findings

Anharmonicity and vertex corrections suppress electron-phonon coupling.

Calculated Tc values match experimental measurements.

Nonadiabatic effects are significant in high-pressure superconductors.

Abstract

Superconductivity in compressed H3S arises from the interplay between high-frequency phonons and a pronounced van Hove singularity near the Fermi level. Using first-principles calculations, we investigate the superconducting properties of H3S and D3S at 160 and 200 GPa, explicitly incorporating anharmonic lattice dynamics and first-order vertex corrections to electron-phonon (e-ph) interactions, thereby going beyond the Migdal approximation underlying conventional Migdal-Eliashberg theory. We find that both anharmonicity and nonadiabatic vertex corrections suppress the effective e-ph coupling and reduce the superconducting critical temperature (Tc). Calculations performed within the energy-dependent full-bandwidth Eliashberg formalism, including both anharmonic and vertex effects, yield Tc values in close agreement with experimental measurements for D3S at both pressures and for H3S at 200 GPa.