Photoinduced ultrafast dynamics of local nematicity and lattice distortions in FeSe crystals

TL;DR

This study investigates how local lattice distortions and nematic electronic order in FeSe crystals respond to ultrafast photoexcitation, revealing a complex coupling between lattice and electronic nematicity.

Contribution

It provides new insights into the local structural dynamics and their interaction with electronic nematicity in FeSe using ultrafast diffraction and microscopy techniques.

Findings

Local lattice distortions exist above the nematic transition temperature.

Photoexcitation releases local lattice distortions, enhancing crystalline order.

A strong coupling between lattice distortions and nematic order is demonstrated.

Abstract

Formation of electronic nematicity is a common thread of unconventional superconductors. In iron-based materials, the long-range nematic order is revealed by the orthorhombic lattice distortion, which importance is a highly controversial topic due the small magnitude of the distortion. Here, we study the local crystal structure of FeSe and its interaction with electronic degrees of freedom using ultrafast electron diffraction, x-ray pair distribution function analysis, and transmission electron microscopy and find a significant lattice response to local nematicity. The study demonstrates how local lattice distortions, which exist even at temperatures above the nematic phase transition, can be released by photoexcitation, leading to an enhancement of the crystalline order. The observed local atomic structures and their out-of-equilibrium behavior unravel a sophisticated coupling between the lattice and nematic order parameter in FeSe.