A possible explanation for double-peak structure in strain dependence of critical current density in REBa2Cu3O coated conductors

Abstract

REBa2Cu3O coated conductors (REBCO-CCs; RE: rare-earth element or Y) have garnered considerable attention in high-field magnet applications. However, the twin structure existing in the ab plane of REBCO complicates the dependence of critical current density on temperature, magnetic field, and uniaxial strain: . In particular, the mechanism for the appearance of anomalous double-peak structure in is unclear.In this study, to understand the complicated strain dependence of critical current density, we measured of REBCO-CCs with c-axis-correlated pins or with random pins as a function of in-plane uniaxial strain and magnetic field applied parallel to the c axis. In the case of (Y,Gd)BCO-CC with BaZrO3 nanorods, we only observed a mountain-shaped response of under the entire magnetic field. However, GdBCO-CC without artificial pinning centers, where random pinning is dominant, exhibited a valley-shaped response at low fields and then a mountain-shaped response at high fields. These results suggest that the variation in the pinning mechanism (correlated- or random pins) plays a crucial role in the absence/presence of double-peak structure in REBCO-CCs.We developed a phenomenological model for in which (i) strain dependence of superconducting properties in two domains of REBCO and (ii) ideal behavior of correlated- or random pinning are considered. Consequently, we observed that the valley-shaped response of can be realized in the case of ideal random pinning with limited parameters, while ideal correlated pinning always exhibits a mountain-shaped response of . Furthermore, a crossover from a valley-shaped response under low fields to a mountain-shaped response under high fields in the strain dependence of is qualitatively consistent with our observations. This qualitative agreement between our model and experimental data validates the efficacy of our model to provide a clear understanding of the strain dependence of in REBCO-CCs, including the anomalous double-peak structure.