Nematic quantum critical point without magnetism in FeSe1-xSx superconductors

TL;DR

This study identifies a nematic quantum critical point in FeSe$_{1-x}$S$_{x}$ superconductors where nematic fluctuations are maximized without magnetic order, providing a unique platform to explore nematicity's role in superconductivity.

Contribution

The paper demonstrates the existence of a nematic quantum critical point in FeSe$_{1-x}$S$_{x}$ without magnetic order, highlighting a new system to study nematic effects on superconductivity.

Findings

Nematic fluctuations are strongly enhanced near the critical composition.

Nematic susceptibility diverges at the quantum critical point.

FeSe$_{1-x}$S$_{x}$ exhibits nematic order without magnetic order.

Abstract

The importance of antiferromagnetic fluctuations are widely acknowledged in most unconventional superconductors. In addition, cuprates and iron pnictides often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. However, these nematic correlations are intertwined with antiferromagnetic or charge orders, preventing us to identify the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe$_{1-x}$S$_{x}$ superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulphur content $x$, whereas the nematic fluctuations are strongly enhanced. Near $x\approx0.17$, the nematic susceptibility diverges towards absolute zero, revealing a nematic quantum critical point. This highlights FeSe$_{1-x}$S$_{x}$ as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.