Strong correlation behavior and Strong coupling superconductivity in (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix with the rich magnetic element Ni

TL;DR

This study investigates Ni-doped (TiHfNbTa) high-entropy alloys, revealing they are strongly coupled bulk superconductors with enhanced Tc and strong electron correlations, offering insights into unconventional superconductivity.

Contribution

It demonstrates that Ni-doped (TiHfNbTa) high-entropy alloys are strongly coupled superconductors with high Tc and strong electron correlations, expanding understanding of unconventional superconductivity in disordered systems.

Findings

(Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix are bulk type-II superconductors

Superconducting transition temperature Tc increases with Ni content

Specific heat jump exceeds BCS value, indicating strong coupling

Abstract

Searching for new superconductors, especially unconventional superconductors, has been studied extensively for decades but remains one of the major outstanding challenges in condensed matter physics. Medium/high-entropy alloys (MEAs-HEAs) are new fertile soils of unconventional superconductors and generate widespread interest and questions on the existence of superconductivity in highly disordered materials. Here, we report on the effect of Ni-doped on the crystal structure and superconductivity properties of strongly coupled TiHfNbTa MEA. XRD results indicate that the maximum solid solution of (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix is about 7.7%. Resistivity, magnetic susceptibility, and specific heat measurements demonstrated that (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEAs are all bulk type-II superconductors and follow the trend of the increase of Tc with the increase of Ni-doped contents. The specific heat jump of all (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix are much larger than the BCS value of 1.43, suggesting all these HEAs are strongly coupled superconductors. Additionally, large Kadawaki-Woods ratio values suggest that there is a strong electron correlation effect in this system. The (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEA system is a new ideal material platform for the study of strong correlation behavior and strongly coupled superconductivity, which provides an insight into the physics of high-temperature superconductors or other unconventional superconductors.