BaFe2As2 Surface Domains and Domain Walls: Mirroring the Bulk Spin Structure

TL;DR

This study uses high-resolution STM to reveal that surface electronic structures of BaFe2As2 reflect the bulk spin order, showing differences from the bulk due to electronic effects rather than geometric surface structure.

Contribution

It demonstrates that surface electronic topography in BaFe2As2 mirrors the bulk spin structure through strong orbital-spin coupling, providing new insights into surface-bulk relationships.

Findings

Surface shows a (1x1) As-terminated unit cell with one As atom imaged.

Domain walls exhibit C2 symmetry, differing from expected geometric symmetry.

Surface electronic features mirror the bulk spin structure via orbital-spin coupling.

Abstract

High-resolution scanning tunneling microscopy (STM) measurements on BaFe2As2-one of the parent compounds of the iron-based superconductors-reveals a (1x1) As-terminated unit cell on the (001) surface. However, there are significant differences of the surface unit cell compared to the bulk: only one of the two As atoms in the unit cell is imaged and domain walls between different (1x1) regions display a C2 symmetry at the surface. It should have been C2v if the STM image reflected the geometric structure of the surface or the orthorhombic bulk. The inequivalent As atoms and the bias dependence of the domain walls indicate that the origin of the STM image is primarily electronic not geometric. We argue that the surface electronic topography mirrors the bulk spin structure of BaFe2As2, via strong orbital-spin coupling.