  High-entropy alloy (HEA) is an attracting topic raising in materials science
and condensed matter physics. Although several types of superconductors have
been discovered in HEAs, the critical currents (Jc) of HEA superconductors
remain uncharacterized up to now. Here, we systematically study the
current-carrying ability of (TaNb)0.7(HfZrTi)0.5 HEA at various heat treatment
conditions. We obtained the high upper critical field and large current
carrying ability, which point to optimistic applications. Interestingly, the
fishtail or second peak effect was found for the first time in HEA
superconductors, and the position of the vortex pinning force shows a maximum
at 0.72 of the reduced field, which is quite different from the cuprates and
iron-based high-Tc superconductors. Together with the resistive measurements,
the vortex phase diagram is obtained for HEA superconductor.
