Intrinsic pinning of FeSe$_1$$_-$$_x$S$_x$ single crystals probed by torque magnetometry

TL;DR

This study uses torque magnetometry to investigate intrinsic pinning mechanisms in FeSe$_{1-x}$S$_x$ superconducting crystals, revealing effects related to gap nodes, twin domains, and layered structure that influence their magnetic properties.

Contribution

It provides new insights into intrinsic pinning in FeSe$_{1-x}$S$_x$ superconductors through angle-resolved torque measurements, highlighting the roles of gap nodes and layered structure.

Findings

Fourfold in-plane torque signal indicating intrinsic pinning

Out-of-plane torque peaks linked to layered structure

Intrinsic pinning influenced by gap nodes and twin domains

Abstract

Intrinsic pinning is caused by natural pinning centers that occur because of the modulation of the order parameter or weak superconducting layers. Early work has shown that intrinsic pinning generates a high pinning force and critical current density in some layered oxide superconductors. Studying the intrinsic pinning of superconductors is crucial for both fundamental studies and potential applications. Herein, we use torque magnetometry to study angle-resolved in-plane and out-of-plane magnetic torque for a series of high-quality FeSe$_1$$_-$$_x$S$_x$ single crystals. A fourfold torque signal was observed when the magnetic field was within the \textit{ab} plane. We interpret that this fourfold in-plane irreversible torque is from the intrinsic pinning due to combined effects of gap nodes/minimum and twin domains. Additionally, we attributed the observed out-of-plane torque peaks to intrinsic pinning due to the layered structure.