Electronic-Structure Correlations Governing Superconductivity in Nb-Based High-Entropy Alloys

TL;DR

This study investigates how electronic structure and lattice disorder influence superconductivity in Nb-based high-entropy alloys, revealing that electronic factors primarily govern critical properties while lattice distortion plays a secondary role.

Contribution

The paper provides a systematic analysis linking electronic structure and lattice distortion to superconductivity, introducing a correlation map for designing high-entropy alloys with improved superconducting properties.

Findings

Superconducting properties evolve non-monotonically with alloy complexity.

Greater lattice distortion can still lead to higher critical temperature and upper critical field.

The niobium d-band position relative to the Fermi level is the main factor controlling electron-phonon coupling.

Abstract

Superconducting high-entropy alloys have recently emerged as a new platform for exploring superconductivity in highly disordered metallic systems and may offer advantages for applications requiring mechanical robustness and tolerance to extreme environments. Yet the mechanisms that govern their superconductivity, particularly the roles of lattice distortion and complex local order, both inherent to high-entropy alloys, remain unclear. The conventional valence-electron-concentration rule fails to reliably predict superconducting behavior, motivating a correlation analysis that links performance to electronic structure and lattice disorder. Here, we study a systematic series of niobium-based body-centered-cubic high-entropy alloys, from binary to quinary compositions, designed to investigate the electronic and structural effects and identify the dominant factors controlling superconductivity. Our experimental results reveal that the superconducting critical properties evolve non-monotonically with alloy complexity. Interestingly, alloys with greater lattice distortion can still achieve higher critical temperature and upper critical field. These observations are corroborated by first-principles and Eliashberg analyses, which identify the position of the niobium d-band relative to the Fermi level as the primary driver of electron-phonon coupling, critical temperature, and upper critical field, with lattice distortion serving as a secondary modifier that generally weakens coupling. We consolidate these findings into a detailed correlation map linking superconducting properties to electronic-structure fingerprints and vibrational signatures, establishing a mechanism-informed design strategy for superconducting high-entropy alloys with enhanced critical temperature and field.