Suppression of the superconducting phase in new structures of elemental sulfur at terapascal pressures

Abstract

We perform a computational structure search and study the phase diagram of elemental sulfur up to 100 TPa from first-principles using ab initio random structure searching (airss), discovering six new phases with the transition sequence $\text{bcc}\ensuremath{\rightarrow}I{4}_{1}/acd\ensuremath{\rightarrow}cI16\ensuremath{\rightarrow}\ensuremath{\alpha}\text{-U}\ensuremath{\rightarrow}\text{hcp}\ensuremath{\rightarrow}A15\ensuremath{\rightarrow}\text{bcc}$. The electronic properties and charge density distributions of the new phases are extensively studied. Remarkably, upon transition to the $I{4}_{1}/acd$ phase at 1.24 TPa, the superconducting critical temperature of sulfur abruptly drops from 12 K to just 0.4 K, and above 5 TPa, we find the critical temperature to be zero up to at least 100 TPa. We show that this sudden suppression of superconductivity is coincident with the formation of a sequence of electride phases, which feature significantly reduced electron-phonon coupling and substantial charge localization. Despite ceasing to be a superconductor, sulfur remains metallic up to at least 100 TPa.