# Emergent XY electronic nematicity in iron-based superconductors

## TL;DR

This paper reports the discovery of nearly isotropic XY-nematic fluctuations in hole-doped iron-based superconductors, revealing a new quantum liquid-crystalline state with potential for unique physical phenomena.

## Contribution

It provides experimental evidence of XY-nematic fluctuations in iron-based superconductors, a state previously considered elusive, using elastoresistance measurements across different doping levels.

## Key findings

- Observation of nearly isotropic XY-nematic fluctuations.
- Doping-dependent orientation of the nematic director.
- Comparable Curie-Weiss behavior in two nematic channels.

## Abstract

Electronic nematicity, a correlated state that spontaneously breaks rotational symmetry, is observed in several layered quantum materials. In contrast to their liquid-crystal counterparts, the nematic director cannot usually point in an arbitrary direction (XY nematics), but is locked by the crystal to discrete directions (Ising nematics),resulting in strongly anisotropic fluctuations above the transition. Here, we report on the observation of nearly isotropic XY-nematic fluctuations, via elastoresistance measurements, in hole-doped Ba$_{1-x}$Rb$_{x}$Fe$_{2}$As$_{2}$ iron-based superconductors. While for $x=0$ the nematic director points along the in-plane diagonals of the tetragonal lattice, for $x=1$ it points along the horizontal and vertical axes. Remarkably, for intermediate doping, the susceptibilities of these two symmetry-irreducible nematic channels display comparable Curie-Weiss behavior, thus revealing a nearly XY-nematic state. This opens a new route to assess this elusive electronic quantum liquid-crystalline state, which is a candidate to host unique phenomena not present in the Ising-nematic case.