Nematicity and magnetism in LaFeAsO single crystals probed by $^{75}$As nuclear magnetic resonance

TL;DR

This study uses $^{75}$As NMR to investigate nematic and magnetic transitions in LaFeAsO single crystals, revealing that nematic order enhances spin fluctuations and is driven by electronic symmetry breaking.

Contribution

It provides the first detailed NMR evidence linking nematic order to spin fluctuations and symmetry breaking in LaFeAsO, comparable to FeSe, regardless of magnetic order presence.

Findings

NMR line splitting indicates electronic rotational symmetry breaking.

Spin fluctuations are strongly enhanced below the nematic transition.

Nematicity promotes spin fluctuations in LaFeAsO, similar to FeSe.

Abstract

We report a $^{75}$As nuclear magnetic resonance study in LaFeAsO single crystals, which undergoes nematic and antiferromagnetic transitions at $T_\text{nem}\sim 156$ K and $T_N \sim 138$ K, respectively. Below $T_\text{nem}$, the $^{75}$As spectrum splits sharply into two for an external magnetic field parallel to the orthorhombic $a$ or $b$ axis in the FeAs planes. Our analysis of the data demonstrates that the NMR line splitting arises from an electronically driven rotational symmetry breaking. The $^{75}$As spin-lattice relaxation rate as a function of temperature shows that spin fluctuations are strongly enhanced just below $T_\text{nem}$. These NMR findings indicate that nematic order promotes spin fluctuations in magnetically ordered LaFeAsO, as observed in non-magnetic and superconducting FeSe. We conclude that the origin of nematicity is identical in both FeSe and LaFeAsO regardless of whether or not a long range magnetic order develops in the nematic state.