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

We report a As75 nuclear magnetic resonance study in LaFeAsO single crystals, which undergoes nematic and antiferromagnetic transitions at Tnem∼156 K and TN∼138 K, respectively. Below Tnem, the As75 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 As75 spin-lattice relaxation rate as a function of temperature shows that spin fluctuations are strongly enhanced just below Tnem. 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. © 2018 American Physical Society1111sciescopu