Superconductivity with large upper critical field in noncentrosymmetric Cr-bearing high-entropy alloys

TL;DR

This study reports the synthesis and characterization of noncentrosymmetric Cr-bearing high-entropy alloys that exhibit bulk superconductivity with upper critical fields near the Pauli limit, highlighting their potential for high-field applications.

Contribution

It introduces a new series of Cr-based high-entropy alloys with noncentrosymmetric structures showing high upper critical fields close to the Pauli limit, which is a novel finding in this material class.

Findings

Superconductivity observed in Cr$_{5+x}$Mo$_{35-x}$W$_{12}$Re$_{35}$Ru$_{13}$C$_{20}$ HEAs.

Upper critical field $B_{c2}(0)$ approaches the Pauli limit, with a maximum ratio of ~1.03.

Superconducting transition temperature decreases with increasing Cr content due to magnetic pair breaking.

Abstract

A series of new Cr$_{5+x}$Mo$_{35-x}$W$_{12}$Re$_{35}$Ru$_{13}$C$_{20}$ high-entropy alloys (HEAs) have been synthesized and characterized by x-ray diffraction, scanning electron microscopy, electrical resistivity, magnetic susceptibility and specific heat measurements. It is found that the HEAs adopt a noncentrosymmetric cubic $\beta$-Mn type structure and exhibit bulk superconductivity for 0 $\leq$ $x$ $\leq$ 9. With increasing $x$, the cubic lattice parameter decreases from 6.7940(3) {\AA} to 6.7516(3) {\AA}. Meanwhile, the superconducting transition temperature $T_{\rm c}$ is suppressed from 5.49 K to 3.35 K due to the magnetic pair breaking caused by Cr moments. For all these noncentrosymmetric HEAs, the zero-temperature upper critical field $B_{\rm c2}$(0) is comparable to Pauli paramagnetic limit $B_{\rm P}$(0) = 1.86$T_{\rm c}$. In particular, the $B_{\rm c2}$(0)/$B_{\rm P}$(0) ratio reaches a maximum of $\sim$1.03 at $x$ = 6, which is among the highest for $\beta$-Mn type superconductors.