Evolution of vortex pinning in the FeSe$_{1-x}$S$_x$ system

TL;DR

This study explores how sulphur doping affects vortex behavior, pinning, and phase transitions in FeSe$_{1-x}$S$_x$, revealing complex pinning interactions, a quasi-2D vortex glass transition, and deviations in critical field predictions.

Contribution

It provides a detailed analysis of vortex matter evolution and pinning mechanisms across different doping levels in FeSe$_{1-x}$S$_x$, including phase diagram and critical field behavior.

Findings

Complex interplay among pinning contributions.

Evidence of a quasi-2D vortex liquid-glass transition.

Upper critical field exceeds WHH model predictions, fitting a two-band model.

Abstract

We present a comprehensive study of vortex matter and pinning evolution in the FeSe$_{1-x}$S$_x$ system with various doping degree. The influence of sulphur substitution on vortex pinning and peak effect occurrence is studied. We show that there is a complex interplay among various pinning contributions in the FeSe$_{1-x}$S$_x$ system. Additionally, we study a possible vortex liquid-vortex glass/lattice transition and find an evidence that the vortex liquid-vortex glass phase transition in FeSe has a quasi two-dimensional nature. We investigate the upper critical field behaviour in FeSe$_{1-x}$S$_x$ system, and found that the upper critical field is higher than that predicted by the Werthamer-Helfand-Hohenberg (WHH) model, whereas its temperature dependence could be fitted within a two-band framework. Finally, a detailed H-T phase diagram is presented.