Controlled disorder-induced peak effect in the single-crystalline Ca3Rh4Sn13 superconductor

The effects of 2.5-MeV electron irradiation on the magnetic properties of single crystals of the Remeika series superconductor Ca3Rh4Sn13 were studied using high-frequency ac susceptometry, magnetization, and electrical transport. This low-pinning cubic stannide is an ideal system to examine the effects of a controlled nonmagnetic pointlike disorder. The measured Campbell penetration depth was used to extract the magnetic field dependence of the unrelaxed critical current density, jc(H). The critical current is a monotonic function of a magnetic field in pristine state. However, even the lowest dose of electron irradiation causes a pronounced peak effect in jc(H). The peak effect is also observed in magnetization measurements performed with different characteristic time windows. We conclude that additional defects trigger the appearance of a disordered vortex phase at magnetic fields close to the upper critical field, and the peak effect is the result of a crossover from the weakly distorted low-field vortex lattice to the disordered high-field vortex phase. These results strongly support the static picture of the peak effect formation in Ca3Rh4Sn13 in which this is a feature of the critical current density, jc(H), and not the result of magnetic field-dependent vortex relaxation, j(H,t).