Atomically Resolved FeSe/SrTiO3(001) Interface Structure by Scanning Transmission Electron Microscopy

TL;DR

This study uses advanced microscopy techniques to reveal the atomic structure of the FeSe/SrTiO3 interface, linking structural details to superconducting properties, thus advancing understanding of high-temperature superconductivity mechanisms.

Contribution

It provides the first atomically resolved structural analysis of the FeSe/SrTiO3 interface in both superconducting and non-superconducting states, highlighting atomic displacements and interface shifts.

Findings

Identification of TiO2 double layers at the interface

Atomic displacements correlate with superconductivity

Lattice compression of FeSe layers

Abstract

Interface-enhanced high-temperature superconductivity in one unit-cell (UC) FeSe films on SrTiO3(001) (STO) substrate has recently attracted much attention in condensed matter physics and material science. By combined in-situ scanning tunneling microscopy/spectroscopy (STM/STS) and ex-situ scanning transmission electron microscopy (STEM) studies, we report on atomically resolved structure including both lattice constants and actual atomic positions of the FeSe/STO interface under both non-superconducting and superconducting states. We observed TiO2 double layers (DLs) and significant atomic displacements in the top two layers of STO, lattice compression of the Se-Fe-Se triple layer, and relative shift between bottom Se and topmost Ti atoms. By imaging the interface structures under various superconducting states, we unveil a close correlation between interface structure and superconductivity. Our atomic-scale identification of FeSe/STO interface structure provides useful information on investigating the pairing mechanism of this interface-enhanced high-temperature superconducting system.