X-ray Diffraction and Equation of State of the C-S-H Room-Temperature Superconductor

TL;DR

This study reveals the structure and properties of a room-temperature superconductor, C-S-H, formed from van der Waals compounds, with a critical temperature of 288 K at high pressure, and discusses its formation, stability, and potential for enhanced superconductivity.

Contribution

It provides the first detailed structural analysis of the C-S-H superconductor, linking its structure to known van der Waals compounds and suggesting mechanisms for its high critical temperature.

Findings

Superconducting phase has orthorhombic structure derived from Al2Cu-type.

Critical temperature of 288 K at 267 GPa.

Structure stability related to similar volumes of H2S and CH4 components.

Abstract

X-ray diffraction indicates that the structure of the recently discovered room temperature carbonaceous sulfur hydride (C-S-H) superconductor is derived from previously established van der Waals compounds found in the H$_2$S-H$_2$ and CH$_4$-H$_2$ systems. Crystals of the superconducting phase were produced by a photochemical synthesis technique leading to the superconducting critical temperature $T_c$ of 288 K at 267 GPa. Single-crystal x-ray diffraction patterns measured from 124 to 178 GPa, within the pressure range of the superconducting phase, give an orthorhombic structure derived from the Al$_2$Cu-type determined for (H$_2$S)$_2$H$_2$ and (CH$_4$)$_2$H$_2$ that differs from those predicted and observed for the S-H system to these pressures. The formation and stability of the C-S-H compound can be understood in terms of the close similarity in effective volumes of the H$_2$S and CH$_4$ components over a broad range of pressures. The relative amounts of carbon and sulfur in the structure is not determined, and denser carbon-bearing S-H structures may form at higher pressures. The results are consistent with hole-doping enhancement of $T_c$ by carbon proposed for the room-temperature superconductivity in this system.