NMR Search for the Spin Nematic State in LaFeAsO Single Crystal

TL;DR

This study uses NMR to investigate LaFeAsO, revealing a spin nematic state with anisotropic spin dynamics that transition into a spin density wave, providing insights into the magnetic properties of this high-temperature superconductor parent compound.

Contribution

First NMR evidence of a spin nematic state in LaFeAsO, showing the development of anisotropic spin dynamics and their evolution into a spin density wave.

Findings

Strong two-fold anisotropy in spin dynamics below T[TO]

Progressive freezing into a spin density wave below T[SDW]

Evidence for a spin nematic state with incipient magnetic order

Abstract

We report a 75-As single crystal NMR investigation of LaFeAsO, the parent phase of a pnictide high Tc superconductor. We demonstrate that spin dynamics develop a strong two-fold anisotropy within each orthorhombic domain below the tetragonal-orthorhombic structural phase transition at T[TO]~156 K. This intermediate state with a dynamical breaking of the rotational symmetry freezes progressively into a spin density wave (SDW) below T[SDW]~142 K. Our findings are consistent with the presence of a spin nematic state below T[TO] with an incipient magnetic order.