# Photoinduced nematic state in FeSe$_{0.4}$Te$_{0.6}$

## TL;DR

This study demonstrates that ultrafast laser pulses can induce a metastable nematic state in FeSe$_{0.4}$Te$_{0.6}$, revealing new insights into the mechanisms behind nematicity in iron-based superconductors.

## Contribution

The paper shows that photoexcitation can create a nematic state in a compound lacking equilibrium nematic order, challenging existing theories about its origin.

## Key findings

- Photoinduced nematic state observed in FeSe$_{0.4}$Te$_{0.6}$
- Ultrafast pulses can stabilize nematicity without effective photodoping
- Nematicity driven by symmetry perturbation, not low-energy fluctuations

## Abstract

FeSe$_{x}$Te$_{1-x}$ compounds present a complex phase diagram, ranging from the nematicity of FeSe to the $(\pi, \pi)$ magnetism of FeTe. We focus on FeSe$_{0.4}$Te$_{0.6}$, where the nematic ordering is absent at equilibrium. We use a time-resolved approach based on femtosecond light pulses to study the dynamics following photoexcitation in this system. The use of polarization-dependent time- and angle-resolved photoelectron spectroscopy allows us to reveal a photoinduced nematic metastable state, whose stabilization cannot be interpreted in terms of an effective photodoping. We argue that the 1.55 eV photon-energy-pump-pulse perturbs the $C_4$ symmetry of the system triggering the realization of the nematic state. The possibility to induce nematicity using an ultra-short pulse sheds a new light on the driving force behind the nematic symmetry breaking in iron-based superconductors. Our results weaken the idea that a low-energy coupling with fluctuations is a necessary condition to stabilize the nematic order and ascribe the origin of the nematic order in iron-based superconductors to a clear tendency of those systems towards orbital differentiation due to strong electronic correlations induced by the Hund's coupling.