High pressure structures of disilane and their superconducting properties

TL;DR

This study uses ab initio methods to identify a new metallic phase of disilane under high pressure, revealing lower superconducting transition temperatures than previously predicted, and questioning the potential for high-T_c superconductivity in hydrogen-rich compounds.

Contribution

The paper introduces a novel metallic phase of disilane with Cmcm symmetry and provides a systematic analysis of its stability and superconducting properties under high pressure.

Findings

Disilane's Cmcm phase is more stable than previous structures up to 280 GPa.

Superconducting T_c decreases from 20 K at 100 GPa to 13 K at 220 GPa.

Predicted T_c values are much lower than earlier estimates, challenging high-T_c claims.

Abstract

A systematic ab initio search for low enthalpy phases of disilane (Si_2H_6) at high pressures was performed based on the minima hopping method. We found a novel metallic phase of disilane with Cmcm symmetry, which is enthalpically more favorable than the recently proposed structures of disilane up to 280 GPa, but revealing compositional instability below 190 GPa. The Cmcm phase has a moderate electron-phonon coupling yielding a superconducting transition temperature T_c of around 20 K at 100 GPa, decreasing to 13 K at 220 GPa. These values are an order of magnitude smaller than previously predicted T_c for disilane, and cast strong doubts on the possibility of high-T_c superconductivity in these systems as well as in other hydrogen-rich compounds under moderate pressure.