Lattice-Shifted Nematic Quantum Critical Point in FeSe$_{1-x}$S$_x$

TL;DR

This study investigates how nematic fluctuations evolve in FeSe$_{1-x}$S$_x$ across a quantum critical point, revealing the influence of lattice coupling and dual electronic contributions on nematic behavior and superconductivity.

Contribution

It demonstrates the impact of nemato-elastic coupling on the nematic QCP and highlights the dual itinerant and local moment nature of nematic fluctuations in Hund's metals.

Findings

Nematic fluctuations show critical behavior only in the low-energy component.

Lattice effects shift the nematic quantum critical point.

No enhancement of superconductivity observed at the QCP.

Abstract

We report the evolution of nematic fluctuations in FeSe$_{1-x}$S$_x$ single crystals as a function of Sulfur content $x$ across the nematic quantum critical point (QCP) $x_c\sim$ 0.17 via Raman scattering. The Raman spectra in the $B_{1g}$ nematic channel consist of two components, but only the low energy one displays clear fingerprints of critical behavior and is attributed to itinerant carriers. Curie-Weiss analysis of the associated nematic susceptibility indicates a substantial effect of nemato-elastic coupling which shifts the location of the nematic QCP. We argue that this lattice-induced shift likely explains the absence of any enhancement of the superconducting transition temperature at the QCP. The presence of two components in the nematic fluctuations spectrum is attributed to the dual aspect of electronic degrees of freedom in Hund's metals, with both itinerant carriers and local moments contributing to the nematic susceptibility.