Disentangling electronic and phononic contributions to high-temperature superconductivity in X2MH6 hydrides

TL;DR

This study analyzes how electronic and phononic factors influence high-temperature superconductivity in X2MH6 hydrides, revealing electronic effects as dominant and providing insights for designing new superconductors.

Contribution

It uniquely disentangles electronic and phononic contributions to Tc in X2MH6 hydrides, identifying key factors affecting superconductivity and their interplay under pressure.

Findings

Electronic contribution dominates Tc in X2MH6 hydrides.

Key factors include X-H bond distance, hydrogen electron localization, and density of states.

Pressure effects are competing, enhancing electronic but weakening phononic contributions.

Abstract

Understanding the factors that control superconductivity is essential for discovering new superconducting materials using high-throughput elemental substitution. Focusing on the recently predicted ambient-pressure superconducting X2MH6 family, we disentangle the phononic and electronic contributions to Tc to determine how isoelectronic substitution alters superconductivity. While substitution affects both phononic and electronic properties, the electronic contribution plays the dominant role in determining Tc in the X2MH6 family. We show that the electronic contribution is affected by three key factors: the X-H bond distance, the electron localization function networking value of hydrogen, and the hydrogen-projected density of states at the Fermi level. A combined figure of merit derived from these parameters exhibits a robust correlation with Tc across the family. We further show that pressure produces competing effects on superconductivity: it enhances the electronic contribution by shortening X-H bonds, but simultaneously weaken the phononic contribution by increasing phonon frequencies. The net pressure dependence of Tc therefore results from the balance between these opposing tendencies. By disentangling and analyzing the electronic and phononic mechanisms, this work provides comprehensive insight into superconductivity in X2MH6 hydrides and offers practical guidance for designing new high-Tc hydride superconductors.