NMR evidence for static local nematicity and its cooperative interplay with low-energy magnetic fluctuations in FeSe under pressure

TL;DR

This study uses NMR to reveal that static local nematicity exists above the bulk transition in FeSe and cooperates with magnetic fluctuations, unaffected by pressure up to 2 GPa.

Contribution

It provides direct microscopic evidence of static local nematic order above the bulk transition and its cooperative relationship with magnetic fluctuations in FeSe under pressure.

Findings

Static local nematic order exists above the bulk transition temperature.

Nematic order and magnetic fluctuations are pressure-insensitive.

Microscopic cooperation between magnetism and nematicity is confirmed.

Abstract

We present $^{77}$Se-NMR measurements on single-crystalline FeSe under pressures up to 2 GPa. Based on the observation of the splitting and broadening of the NMR spectrum due to structural twin domains, we discovered that static, local nematic ordering exists well above the bulk nematic ordering temperature, $T_{\rm s}$. The static, local nematic order and the low-energy stripe-type antiferromagnetic spin fluctuations, as revealed by NMR spin-lattice relaxation rate measurements, are both insensitive to pressure application. These NMR results provide clear evidence for the microscopic cooperation between magnetism and local nematicity in FeSe.