Nematicity and magnetism in LaFeAsO single crystals probed by As-75 nuclear magnetic resonance

Abstract

We report a As-75 nuclear magnetic resonance study in LaFeAsO single crystals, which undergoes nematic and antiferromagnetic transitions at T-nem similar to 156 K and T-N similar to 138 K, respectively. Below T-nem, the As-75 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 As-75 spin-lattice relaxation rate as a function of temperature shows that spin fluctuations are strongly enhanced just below T-nem. These NMR findings indicate that nematic order promotes spin fluctuations in magnetically ordered LaFeAsO, as observed in nonmagnetic 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.