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

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.

Figures (10)

• Figure 1: (a-d) $T_{\rm{c}}$ (top) and $J_{\rm{c}}$ (bottom) as functions of doping concentration ($x$) or pressure ($P$) in Y$_{0.8}$Ca$_{0.2}$Ba$_{2}$Cu$_{3}$O$_{y}$talantsev2014holetallon1999criticalnaqib2019possible, Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$hecher2018direct, heavy-fermion superconductor CeRhIn$_{5}$jung2018peak, and the kagome superconductor CsV$_{3}$Sb$_{5}$wang2024quantum. The dot-dashed lines indicate the locations of the QCP (or the endpoint of the ordered phase).
• Figure 2: (a) The complete phase diagram of FeSe$_{1-x}$(Te/S)$_{x}$ single crystals. Black lines, solid circles, and squares correspond to $T_{\rm{s}}$, $T_{\rm{c}}$, and $T_{\rm{N}}$, respectively. The open stars represent the $T_{\rm{c}}$($x$) values from Ref.mukasa2023enhanced. (b) Contour plot of $J_{\rm{c}}$ for FeSe$_{1-x}$(Te/S)$_{x}$ at a normalized temperature under self-field ($H$ = 0 T). The color represents the scale of the critical current density. The $J_{\rm{c}}$ at zero magnetic field for FeSe$_{0.96}$S$_{0.04}$ is derived from the study of Mahmoud Abdel-Hafiez $et$$al$. abdel2015superconducting.
• Figure 3: (a) Images of FeSe$_{1-x}$(Te/S)$_{x}$ single crystals; (b) The EDX spectrum (top panel) and compositional mappings (bottom panels) of Fe, Se, and Te within the selected rectangular region are shown for a representative FeSe$_{0.72}$Te$_{0.28}$ single crystal; (c) Temperature dependence of the normalized resistivity, $\rho$($T$)/$\rho$(200 K), for different FeSe$_{1-x}$(Te/S)$_{x}$ single crystals. The orange and pink arrows indicate the nematic ($T_{\rm{s}}$) and antiferromagnetic transitions ($T_{\rm{N} }$), respectively; (d) Temperature dependences of ZFC magnetizations at 5 Oe parallel to $c$-axis for FeSe$_{1-x}$(Te/S)$_{x}$ single crystals.
• Figure 4: (a-i) The dependencies of $J_{\rm{c}}$ on temperature ($T$) and magnetic field ($H$) for (a) FeSe$_{0.77}$S$_{0.23}$, (b) FeSe$_{0.85}$S$_{0.15}$, (c) FeSe$_{0.92}$S$_{0.08}$, (d) FeSe, (e) FeSe$_{0.89}$Te$_{0.11}$, (f) FeSe$_{0.85}$Te$_{0.15}$, (g) FeSe$_{0.65}$Te$_{0.35}$, (h) FeSe$_{0.5}$Te$_{0.5}$, (i) FeSe$_{0.4}$Te$_{0.6}$, (j) FeSe$_{0.3}$Te$_{0.7}$, (k) FeSe$_{0.2}$Te$_{0.8}$, and (l) FeSe$_{0.1}$Te$_{0.9}$ single crystals, respectively.
• Figure 5: $J_{\rm{c}}(t)$ normalized by $J_{\rm{c}}$($t$=0.3) as a function of the reduced temperature $t$ = $T$/$T_{\rm{c}}$ for all the crystals under zero magnetic field. The normalized $J_{\rm{c}}$($t$) collapse onto a universal curve. Blue dashed line and red solid curve are for $\delta T_{\rm{c}}$-pinning and $\delta l$-pinning, respectively.