Tunable Fe-vacancy disorder-order transition in FeSe thin films

TL;DR

This study demonstrates that Fe-vacancy disorder-order transitions in FeSe thin films can be reversibly tuned by vacuum annealing, revealing the ordered phase as a potential parent phase for superconductivity.

Contribution

It provides in-situ ARPES evidence of tunable Fe-vacancy order in FeSe films, linking structural phases to electronic properties and potential superconductivity.

Findings

Fe-vacancy disordered phase is electron doped and metallic.

Long-term low-temperature anneal induces a transition to a (root 5) x (root 5) ordered phase.

High-temperature anneal reverts the ordered phase to disordered.

Abstract

Various Fe-vacancy orders have been reported in tetragonal Fe1-xSe single crystals and nanowires/nanosheets, which are similar to those found in alkali metal intercalated A1-xFe2-ySe2 superconductors. Here we report the in-situ angle-resolved photoemission spectroscopy study of Fe-vacancy disordered and ordered phases in FeSe multi-layer thin films grown by molecular beam epitaxy. Low temperature annealed FeSe films are identified to be Fe-vacancy disordered phase and electron doped. Further long-time low temperature anneal can change the Fe-vacancy disordered phase to ordered phase, which is found to be semiconductor/insulator with (root 5) x (root 5) superstructure and can be reversely changed to disordered phase with high temperature anneal. Our results reveal that the disorder-order transition in FeSe thin films can be simply tuned by vacuum anneal and the (root 5) x (root 5) Fe-vacancy ordered phase is more likely the parent phase of FeSe.