Chemical composition effect on superconductivity in noncentrosymmetric -Mn-type high-entropy alloys

We report the effect of chemical composition variation on the superconductivity in noncentrosymmetric beta-Mn-type high-entropy alloys (HEAs) studied in two very similar Ta5+xMo35-xW5Re35Ru20C20 and Ta5+yW35-yMo5Re35Ru20C20 series. It is found that both HEAs consist of a single cubic beta-Mn-type phase for 0 <= x <= 6 and 0 <= y <= 9. Bulk fully gapped superconductivity is observed for all these HEAs and their zero-temperature upper critical fields approach the Pauli paramagnetic limit. While our analysis suggests that T-c of these HEAs is mainly controlled by the electron-phonon coupling strength, T-c of the Ta5+xMo35-xW5Re35Ru20C20 series is always higher than that of the Ta5+yW35-yMo5Re35Ru20C20 one even for (nearly) the same valence electron concentration and unit-cell volume. This difference is attributed to the different contributions of Mo and W to the electronic structure, which is supported by the first-principles calculations. Our study suggests that the chemical composition effect should be considered to better understand the superconducting behavior in noncentrosymmetric HEAs.