Boost of critical current density near quantum critical points in FeSe-Based superconductors with two superconducting domes

TL;DR

This study investigates how the critical current density in FeSe-based superconductors peaks near quantum critical points associated with nematic phases, revealing three maxima and suggesting an ordered phase endpoint beneath the superconducting dome.

Contribution

It uncovers three maxima of critical current density in FeSe-based superconductors and links these peaks to nematic quantum critical points and vortex pinning mechanisms, advancing understanding of quantum critical effects.

Findings

Two sharp peaks of $J_{c}$ at nematic phase endpoints.

Three maxima of $J_{c}$ observed across two superconducting domes.

Enhanced $J_{c}$ near FeSe$_{0.1}$Te$_{0.9}$ indicating possible ordered phase endpoint.

Abstract

Recent studies have identified two superconducting domes in FeSe-based superconductors. It was discovered that each dome is accompanied by a distinct nematic quantum critical point (QCP): one associated with a pure nematic QCP, and the other with a nematic QCP entangled with antiferromagnetism (AFM). In this study, we delve into the evolution of the critical current density ($J_{\rm{c}}$) with doping in FeSe${_{1-x}}$(Te/S)${_{x}}$ single crystals, focusing on the behavior within the two superconducting domes. Surprisingly, three maxima of $J_{\rm{c}}$ were found in the two superconducting domes, with two sharp peaks in $J_{\rm{c}}$ observed precisely at the endpoints of the nematic phases, at $x$(Te) $\sim$ 0.5 for Te-doped and $x$(S) $\sim$ 0.17 for S-doped FeSe. The mechanisms of vortex pinning and the influence of quantum critical fluctuations have been extensively explored, emphasizing the contribution of quantum critical fluctuations in modulating $J_{\rm{c}}$. Additionally, an increase in $J_{\rm{c}}$ was also noted near FeSe$_{0.1}$Te$_{0.9}$, where its origin has been explored and discussed. This finding provides crucial clues about the existence of an ordered phase endpoint beneath the superconducting dome, offering an initial basis for further investigation into the potential presence of a QCP beneath it.