Nanoscale decoupling of electronic nematicity and structural anisotropy in FeSe thin films

TL;DR

This study demonstrates that in FeSe thin films, electronic nematicity can be locally decoupled from structural anisotropy, revealing a nanoscale stiffness of the nematic order parameter through strain engineering and local spectroscopic analysis.

Contribution

It provides the first evidence of nanoscale decoupling between electronic nematicity and structural anisotropy in strain-engineered FeSe thin films.

Findings

Electronic nematicity can be locally decoupled from structural anisotropy.

Nanoscale regions show nematic order that does not follow structural reversals.

Nematic order parameter exhibits nanometer-scale stiffness.

Abstract

In a material prone to a nematic instability, anisotropic strain in principle provides a preferred symmetry-breaking direction for the electronic nematic state to follow. This is consistent with experimental observations, where electronic nematicity and structural anisotropy typically appear hand-in-hand. In this work, we discover that electronic nematicity can be locally decoupled from the underlying structural anisotropy in strain-engineered iron-selenide (FeSe) thin films. We use heteroepitaxial molecular beam epitaxy to grow FeSe with a nanoscale network of modulations that give rise to spatially varying strain. We map local anisotropic strain by analyzing scanning tunneling microscopy topographs, and visualize electronic nematic domains from concomitant spectroscopic maps. While the domains form so that the energy of nemato-elastic coupling is minimized, we observe distinct regions where electronic nematic ordering fails to flip direction, even though the underlying structural anisotropy is locally reversed. The findings point towards a nanometer-scale stiffness of the nematic order parameter.