Study of minor hysteresis loops in the usual and anomalous superconducting regime of (Ce_0.95Nd_0.05)Ru₂: evidence of a First-order transition

Abstract

We present a detailed study of minor hysteresis loops (MHLs) in the usual and anomalous superconducting (SC) regime of (Ce_0.95Nd_0.05)Ru₂. MHLs in the usual SC regime follow the predictions of critical state models (CSM) for a hard type-II SC with field-dependent critical current (J_c). At the onset of the anomalous SC regime, the behaviour of the MHLs cannot be explained by CSM alone. Our results present strong evidence of a first-order transition from the usual to the anomalous SC phase. MHLs are used to track the growth of the domains or nuclei of the anomalous SC phase across this first-order transition. Well inside the anomalous regime where the first-order transition is complete, MHLs are again as expected from CSM and this behaviour persists until one reaches the reversible regime below H_c2, indicating that the upper transition is of second order.