Phase diagram of the sulfur hydride: transition into high Tc state

TL;DR

This paper investigates the phase transition in sulfur hydride responsible for its high critical temperature, revealing it as a first-order transition causing Fermi surface changes and a two-gap spectrum.

Contribution

It provides a symmetry-based analysis showing the transition is first order, linking structural changes to electronic properties in sulfur hydride.

Findings

Transition is first order, not second order.

Structural transition causes Fermi surface pockets.

Results explain the high Tc in sulfur hydride.

Abstract

Remarkable feature of the phase diagram of sulfur hydrides is a sharp increase in critical temperature from 120K up to200K. This increase is a signature of the structural transition. The study described below is concerned with the nature of this phase transition. One can demonstrate that the symmetry analysis along with an analysis of the impact of lattice deformations lead to the conclusion that we are dealing with the first order transition. It leads to an abrupt appearance of small pockets on the Fermi surface and to the two-gap energy spectrum.