First-principles study of the pressure and crystal-structure dependences of the superconducting transition temperature in compressed sulfur hydrides

TL;DR

This study uses first-principles calculations to analyze how pressure and crystal structure influence the superconducting transition temperature in compressed sulfur hydrides, reproducing experimental results and predicting potential higher-$T_c$ phases.

Contribution

It provides a detailed first-principles analysis of pressure and structure effects on $T_c$ in sulfur hydrides, including isotope effects and phase competition, advancing understanding of high-temperature superconductivity.

Findings

Reproduces experimental $T_c$ values at pressures below 150 GPa.

Predicts higher $T_c$ in $Im3m$-H$_{3}$S at higher pressures.

Shows isotope effect coefficient can exceed 0.5 due to phase competition.

Abstract

We calculate superconducting transition temperatures ($T_{\rm c}$) in sulfur hydrides H$_{2}$S and H$_{3}$S from first principles using the density functional theory for superconductors. At pressures of $\lesssim$150 GPa, the high values of $T_{\rm c}$ ($\gtrsim$130 K) observed in the recent experiment [A. P. Drozdov, M. I. Eremets, and I. A. Troyan, arXiv:1412.0460] are accurately reproduced by assuming that H$_{2}$S decomposes into $R3m$-H$_{3}$S and S. For the higher pressures, the calculated $T_{\rm c}$s for $Im3m$-H$_{3}$S are systematically higher than those for $R3m$-H$_{3}$S and the experimentally observed maximum value (190 K), which suggests the possibility of another higher-$T_{\rm c}$ phase. We also quantify the isotope effect from first principles and demonstrate that the isotope effect coefficient can be larger than the conventional value (0.5) when multiple structural phases energetically compete.