Bounds on nanoscale nematicity in single-layer FeSe/SrTiO[subscript 3]

Abstract

We use scanning tunneling microscopy (STM) and quasiparticle interference (QPI) imaging to investigate the low-energy orbital texture of single-layer FeSe/SrTiO[subscript 3]. We develop a T-matrix model of multiorbital QPI to disentangle scattering intensities from Fe 3d[subscript xz] and 3d[subscript 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[subscript 3] film, we quantitatively exclude static xz/yz orbital ordering with domain size larger than δr[superscript 2] = 20 nm × 20 nm, xz/yz Fermi wave vector difference larger than δk = 0.014 π, and energy splitting larger than δE = 3.5 meV. The lack of detectable ordering pinned around defects places qualitative constraints on models of fluctuating nematicity.