Anisotropy of upper critical fields and thermally-activated flux flow of quenched KxFe2-ySe2 single crystals

TL;DR

This study investigates the anisotropic upper critical fields and flux flow behavior in quenched KxFe2-ySe2 single crystals, revealing minor effects of quenching on critical fields and dominant flux creep mechanisms.

Contribution

It provides new insights into the anisotropic superconducting properties and flux pinning mechanisms of quenched KxFe2-ySe2, supported by experimental analysis and scaling laws.

Findings

Anisotropy Gamma(T) increases with decreasing temperature, reaching ~3.6 at 27 K.

Resistivity follows Arrhenius TAFF behavior for both field directions.

Collective flux creep dominates at high fields with point defects as main pinning centers.

Abstract

We report the anisotropy of the upper critical fields mu0Hc2(T) and thermally-activated flux flow (TAFF) behavior of quenched KxFe2-ySe2. Even though the post-annealing and quenching process enhances the superconducting volume fraction, it has a minor effect on the upper critical fields for H//c and H//ab. Analysis of the angular-dependence of resistivity rho_ab(theta,H) indicates that it follows the scaling law based on the anisotropic Ginzburg-Landau (GL) theory and the anisotropy Gamma(T) increases with decreasing temperature with Gamma(T) ~ 3.6 at 27 K. The resistivity of quenched sample exhibits an Arrhenius TAFF behavior for both field directions. Field dependence of thermally activated energy U0(H) implies that the collective flux creep is dominant in high fields and point defects are the main pinning source in this regime.