Measurements of the superconducting anisotropy in FeSe with a resonance frequency technique

Abstract

Utilizing a novel method with the resonance frequency of a LC circuit, we measured the superconducting anisotropy of single crystals of an Fe-based superconductor FeSe with applied magnetic field up to 16 T. We found that the temperature dependence of the upper critical field H c2 (T) of FeSe coincides with the Werthamer-Helfand-Hohenberg (WHH) model when taking the Maki parameter α into consideration, suggesting an important role played by spin-paramagnetic effect in suppressing the superconductivity. When temperature T → 0, the values of H c2,≈c (0) and H c2,≈ab (0) derived from the WHH fitting are close to and fall within the range of the Pauli limit, for field H 0 applied parallel to the c-axis and to the ab-plane, respectively. As compared with other typical iron-based high-T c superconductors, lower values of H c2 (0) and higher superconducting anisotropy Γ(0) were observed in FeSe. © 2019 Author(s).