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 (∆Cel/γ"T" _"c" ^" mid") of all (Ti 1/4 Hf1/4Nb 1/4 Ta 1/4) 1-x Ni x are much larger than the BCS value of 1. 43, suggesting all these HEAs are strongly coupled superconductors. Additionally, large Kadawaki-Woods ratio (KWR) values suggest that there is a strong electron correlation effect in this system. The (Ti 1/4 Hf1/4Nb 1/4 Ta 1/4) 1-x Ni x 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.
Huang et al. (Mon,) studied this question.