Enhanced Electron-Phonon Coupling and Superconductivity in Ba-Alloyed A15 LaH5.75

TL;DR

This study shows that partial substitution of La with Ba in A15 LaH5.75 enhances electron-phonon coupling and raises the superconducting transition temperature to about 183 K, providing a pathway for designing higher Tc hydride superconductors.

Contribution

It demonstrates that Ba alloying stabilizes A15 LaH5.75 and significantly increases its Tc, extending alloy design principles for high-temperature superconductors.

Findings

Ba substitution stabilizes LaH5.75 structure.

Superconducting Tc increases to approximately 183 K.

Doping shifts Fermi level and enhances electron-phonon coupling.

Abstract

Recent experiments have established rare earth A15 type hydrides as a distinct family of high temperature superconductors that can be stabilized at significantly lower pressures compared to other superconducting hydrides. In particular, A15 type LaH5.75 was recently shown to be a high Tc superconductor. We have investigated a range of ternary substitutions and demonstrate that partial substitution of La by Ba stabilizes the A15 hydride lattice, with La0.75Ba0.25H5.75 identified as a stable compound. We calculate a superconducting transition temperature of approximately 183 K, almost double that of LaH5.75 at similar pressures. Ba typically acts as a 2 plus ion, while La is 3 plus. The reduced electron count disrupts the formation of H2 units and shifts the Fermi surface, leading to strongly enhanced electron phonon coupling. By contrast, substitution with Hf fails to produce any stable compounds. This work extends emerging alloy design principles in A15 hydride superconductors, demonstrating that doping can shift the Fermi level and tune the strength of the electron phonon coupling. These results provide concrete guidance for the experimental realization of new high Tc phases.