First-Principles Study of High-Temperature Superconductivity in X2MH6 Compounds under 20 GPa

TL;DR

This study uses first-principles calculations to identify new high-temperature superconducting compounds in the X2MH6 family under 20 GPa, highlighting the role of atomic substitution and phonon interactions.

Contribution

It discovers 11 stable ternary compounds with three exceeding 100 K, and elucidates mechanisms behind their high superconducting transition temperatures.

Findings

11 stable ternary compounds identified

3 compounds exceed 100 K in Tc

Strong electron-phonon coupling enhances superconductivity

Abstract

Research on high-temperature superconductors has primarily focused on hydrogen-rich compounds, however, the need for extreme pressures limits their practical applications. The X2MH6-type structure Mg2IrH6 stands out because it exhibits superconductivity at 160 K under ambient pressure. This study investigates methods to increase the superconducting transition temperature of this structure via atomic substitution and low-pressure treatment and assess the mechanical, thermodynamic, and dynamic stability of structures obtained by substituting Mg and Ir atoms in Mg2IrH6 with elements from the same groups using first-principles calculations. The findings identify 11 stable ternary compounds, 10 of which exhibit superconducting transition temperatures, with three compounds, Mg2CoH6, Mg2RhH6, and Mg2IrH6, exceeding 100 K, classifying them as high-temperature superconductors. Their superconducting figure of merit S values are 2.71, 3.35, and 3.83, respectively, suggesting strong practical application potential. The analysis results indicate that mid-frequency hydrogen phonons significantly enhance superconducting properties via electron-phonon coupling. The band structure study highlights the importance of van Hove singularities near the Fermi level. In addition, electron localization function and Fermi surface topology analyses reveal that the Fermi surface shape and density of states are crucial for increasing superconducting transition temperatures.