Pressure-induced reconstitution of Fermi surfaces and spin fluctuations in S-substituted FeSe

TL;DR

This study reveals how pressure induces a Lifshitz transition and distinct superconducting phases in S-substituted FeSe, highlighting the role of orbital interactions and magnetic fluctuations in high-temperature superconductivity.

Contribution

It provides the first detailed NMR analysis of pressure effects on S-substituted FeSe, uncovering the Lifshitz transition and dual superconducting domes with different magnetic fluctuation characteristics.

Findings

Lifshitz transition at 1.0 GPa observed via NMR anomalies.

Two superconducting domes with different AF fluctuations identified.

High-$T_c$ dome correlates with weaker AF fluctuations and orbital effects.

Abstract

FeSe is a unique high-$T_c$ iron-based superconductor in which nematicity, superconductivity, and magnetism are entangled with each other in the $P$-$T$ phase diagram. We performed $^{77}$Se-nuclear magnetic resonance measurements under pressures of up to 3.9 GPa on 12% S-substituted FeSe, in which the complex overlap between the nematicity and magnetism are resolved. A pressure-induced Lifshitz transition was observed at 1.0 GPa as an anomaly of the density of states and as double superconducting (SC) domes accompanied by different types of antiferromagnetic (AF) fluctuations. The low-$T_{\rm c}$ SC dome below 1 GPa is accompanied by strong AF fluctuations, whereas the high-$T_{\rm c}$ SC dome develops above 1 GPa, where AF fluctuations are fairly weak. These results suggest the importance of the $d_{xy}$ orbital and its intra-orbital coupling for the high-$T_{\rm c}$ superconductivity.