Atomically resolved FeSe/SrTiO ₃ (001) interface structure by scanning transmission electron microscopy

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 interfaceenhanced high-temperature superconducting system.

Superconductivity above 28 K in single unit cell FeSe films interfaced with GaO2− layer on NdGaO3(1 1 0)

“…These atoms locate directly on top of Ga, but exhibit similar intensity and size. We speculate that the extra layer corresponds to GaO2δ layer, giving rise to a double-GaO2-δ at the interface similar to that observed in FeSe/SrTiO3 [34]. Between this extra layer and FeTe capping layer resides the interfacial Se-Fe-Se triple layer.…”

“…The FeTe films were grown by co-evaporating Fe and Te from standard Knudsen cells at a substrate temperature of 255 °C . This capping method has been successfully used for protecting FeSe films against ambient contamination/oxidation [4,10,34]. STEM samples were prepared using Focused Ion Beam method.…”

Origin of charge transfer and enhanced electron–phonon coupling in single unit-cell FeSe films on SrTiO3

“…The top layer has a larger spectral weight shift due to a larger band bending while the layer deep in the bulk has a negligible energy shift 36 . We employ the up-to-date structural information with double TiO 2 layers of STO at the interface 32, 37 , i.e., TiO 2 /TiO 2 /SrO/TiO 2 /SrO…. Switching to the situation of a single surface TiO 2 layer affects the fitted results but the difference falls within the error bar (Supplementary Fig.…”

High‐Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces

“…This termination is also found by cross‐section scanning transmission electron microscopy. [ 222 ] The double TiO 2 termination leads to a reconstruction of the interfacial layer of SrTiO 3 with a periodicity, which is observed as superstructure peaks in the X‐ray diffraction. DFT calculations point out that stronger electron transfer between the SrTiO 3 and the FeSe is present when the SrTiO 3 has a double TiO 2 termination rather than the usual single TiO 2 layer termination.…”