Crystal structures and high-temperature superconductivity in molybdenum-hydrogen binary system under high pressure

TL;DR

This study explores high-pressure molybdenum-hydrogen compounds, revealing new stable and metastable superconducting structures with transition temperatures up to 126 K, emphasizing the role of non-integer compositions and metastability in superconductor discovery.

Contribution

It provides a comprehensive phase diagram of Mo-H compounds at high pressure and identifies new metastable superconducting structures with high transition temperatures.

Findings

New stable and metastable Mo-H superconducting phases identified.

Superconducting transition temperatures range from 55 to 126 K at 300 GPa.

Vibrations of Mo atoms significantly contribute to electron-phonon coupling.

Abstract

Motivated by advances in hydrogen-rich superconductors in the past decades, we conducted variable-composition structural searches in Mo-H binary system at high pressure. A new composition-pressure phase diagram of thermodynamically stable structures has been derived. Besides all previously discovered superconducting molybdenum hydrides, we also identified series of thermodynamically metastable superconducting structures, including I4/mmm-Mo$_3$H$_{14}$, I4cm-MoH$_9$, P4/nmm-MoH$_{10}$ and P42$_1$2-MoH$_{10}$, with the superconducting transition temperatures from 55 to 126 K at 300 GPa. In these superconducting molybdenum hydrides, vibrations of the Mo-atoms contributes significantly to the electron-phonon coupling and the superconducting transition temperature, in complementary to the contributions by the vibrations of the H-atoms. Our works highlight the importance of compounds with non-integer composition ratio and metastable states in material searches, for example the potential high temperature superconductors.