On the Determination of Pinning Mechanisms and Regimes in Type-II Superconductors with Weak Thermal Fluctuations

Abstract

Determination of pinning mechanisms is an important topic in the study of practical type-II superconductors. In this paper, we modify the underlying assumptions of the conventional model, which is used to determine the pinning mechanisms from the experimental data on the temperature dependence of Jc(T)/Jc(0). The assumption that the vortices are pinned in the single vortex regime and the considered temperature dependencies for λ and ξ and temperature independency for e are not always correct. Inappropriate assumptions may lead the determination of pinning mechanisms to confusing or misleading results by creating a discrepancy between theory and experiment. To resolve the discrepancy and have a model with the ability to be customized for different type-II superconductors and with the capacity to be used at various magnetic fields (in which the vortices may be pinned in the single vortex, small bundle, or large bundle regime), we adopt more general assumptions, by employing the critical current density expressions in different pinning regimes and generalizing the considered temperature dependencies for λ, ξ, and e quantities, and derive an extended model. Afterward, applying the conventional and extended models for the determination of pinning mechanisms in Ba0.66K0.32BiO3 + δ and FeSe superconductor single crystals, in which the thermal fluctuations are weak and js ≈ jc, we demonstrate that the extended model is capable of preventing the determination of pinning mechanisms from leading to confusing or misleading results and can be employed to improve the understanding of pinning mechanisms and regimes in type-II superconductors.