Effect of proton irradiation on the upper critical field and vortex pinning in Kagome superconductor CsV₃Sb₅

The Kagome superconductor CsV₃Sb₅ exhibits an intriguing interplay between charge density wave (CDW) order, superconductivity that can be traced to the presence of van Hove singularities (vHS) and Dirac points in the electronic band structure. Here, we report on the impact of proton irradiation on the superconducting phase boundary and vortex pinning in high-quality single crystal samples. The pristine samples display pronounced upwards curvature in the in-plane and out-of-plane upper critical fields which upon irradiation gives way to the conventional dirty-limit Maki – deGennes variation. We attribute this change to the smearing of the pronounced anisotropy of the electronic band structure arising from the vHS due to strong scattering by irradiation induced defects. Vortex pinning in the pristine sample is almost entirely dominated by surface pinning inducing magnetization hysteresis curves with vanishing magnetization on the return branches, while upon irradiation, a non-monotonic fishtail feature arises in the hysteresis signaling the appearance of substantial bulk pinning. Remarkably, the superconducting transition clearly sharpens upon irradiation.