# Possible Bicollinear Nematic State with Monoclinic Lattice Distortions in Iron Telluride Compounds

## TL;DR

This paper proposes that iron telluride can host a bicollinear nematic state with monoclinic lattice distortions, stabilized by coupling between lattice strain and orbital order, observable above the temperature of full magnetic order.

## Contribution

The study introduces a spin-fermion model with lattice coupling showing how a nematic state can emerge in FeTe, splitting the magnetic transition and stabilizing short-range order.

## Key findings

- Monte Carlo simulations demonstrate transition splitting with increased coupling.
- A monoclinic nematic phase with short-range order is stabilized.
- The lattice distortion and nematicity occur above the magnetic ordering temperature.

## Abstract

Iron telluride FeTe is known to display bicollinear magnetic order at low temperatures together with a monoclinic lattice distortion. Because the bicollinear order can involve two different wavevectors $(\pi/2,\pi/2)$ and $(\pi/2,-\pi/2)$, symmetry considerations allow for the possible stabilization of a nematic state with short-range bicollinear order coupled to monoclinic lattice distortions at a $T_S$ higher than the temperature $T_N$ where long-range bicollinear order fully develops. As a concrete example, the three-orbitals spin-fermion model for iron telluride is studied with an additional coupling $\tilde\lambda_{12}$ between the monoclinic lattice strain and an orbital-nematic order parameter with $B_{2g}$ symmetry. Monte Carlo simulations show that with increasing $\tilde\lambda_{12}$ the first-order transition characteristic of FeTe splits and bicollinear nematicity is stabilized in a (narrow) temperature range. In this new regime the lattice is monoclinically distorted and short-range spin and orbital order breaks rotational invariance. A discussion of possible realizations of this exotic state is provided.