Bounds on Nanoscale Nematicity in Single-Layer FeSe/SrTiO$_3$

TL;DR

This study employs STM and QPI imaging with a developed T-matrix model to quantitatively constrain the presence of static nematic orbital order in single-layer FeSe/SrTiO$_3$, finding no detectable static nematicity above certain thresholds.

Contribution

The paper introduces a T-matrix based QPI analysis method to nanoscale detect and set bounds on static nematic orbital order in FeSe/SrTiO$_3$.

Findings

No static orbital order larger than 20 nm domain size

Fermi wave vector difference less than 0.014 π

Energy splitting less than 3.5 meV

Abstract

We use scanning tunneling microscopy (STM) and quasiparticle interference (QPI) imaging to investigate the low-energy orbital texture of single-layer FeSe/SrTiO$_3$. We develop a $T$-matrix model of multi-orbital QPI to disentangle scattering intensities from Fe $3d_{xz}$ and $3d_{yz}$ bands, enabling the use of STM as a nanoscale detection tool of nematicity. By sampling multiple spatial regions of a single-layer FeSe/SrTiO$_3$ film, we quantitatively exclude static $xz/yz$ orbital ordering with domain size larger than $\delta r^2$ = 20 nm $\times$ 20 nm, $xz/yz$ Fermi wave vector difference larger than $\delta k$ = 0.014 $\pi$, and energy splitting larger than $\delta E$ = 3.5 meV. The lack of detectable ordering pinned around defects places qualitative constraints on models of fluctuating nematicity.