Observation of three-state nematicity in the triangular lattice antiferromagnet Fe$_{1/3}$ NbS$_2$

TL;DR

This paper reports the discovery of a three-state nematic order in the triangular lattice antiferromagnet Fe$_{1/3}$NbS$_2$, revealing a novel Z$_3$ nematic state with potential applications in device technology.

Contribution

It introduces a new three-state nematic order parameter in a crystalline material, expanding the understanding of nematic phases beyond two-state systems.

Findings

Identified three distinct nematic states in Fe$_{1/3}$NbS$_2$

Demonstrated continuous re-orientation of anisotropy axes

Used novel spatially-resolved optical polarimetry technique

Abstract

Nematic order is the breaking of rotational symmetry in the presence of translational invariance. While originally defined in the context of liquid crystals, the concept of nematic order has arisen in crystalline matter with discrete rotational symmetry, most prominently in the tetragonal Fe-based superconductors where the parent state is four-fold symmetric. In this case the nematic director takes on only two directions, and the order parameter in such "Ising-nematic" systems is a simple scalar. Here, using a novel spatially-resolved optical polarimetry technique, we show that a qualitatively distinct nematic state arises in the triangular lattice antiferromagnet Fe$_{1/3}$NbS$_2$. The crucial difference is that the nematic order on the triangular lattice is a Z$_3$, or three-state Potts-nematic order parameter. As a consequence, the anisotropy axes of response functions such as the resistivity tensor can be continuously re-oriented by external perturbations. This discovery provides insight into realizing devices that exploit analogies with nematic liquid crystals.