Fe-vacancy ordered Fe4Se5: The insulating parent phase of FeSe superconductor

TL;DR

This study identifies Fe4Se5 with Fe-vacancy order as an insulating parent phase of FeSe superconductor, showing a transition to superconductivity after vacancy disordering and increased electron carriers.

Contribution

It reveals the role of Fe-vacancy order in FeSe and demonstrates how thermal treatment induces superconductivity without altering chemical composition.

Findings

Fe4Se5 exhibits 3D-Mott variable range hopping behavior.

RTA process destroys Fe-vacancy order and increases electron carriers.

Superconductivity with Tc ~ 8K emerges after vacancy disordering.

Abstract

We have carried out a detailed study to investigate the existence of an insulating parent phase for FeSe superconductor. The insulating Fe4Se5 with specific Fe-vacancy order shows a 3D-Mott variable range hopping behavior with a Verwey-like electronic correlation at around 45 K. The application of the RTA process at 450 celcius degree results in the destruction of Fe-vacancy order and induces more electron carriers by increasing the Fe3+ valence state. Superconductivity emerges with Tc ~ 8K without changing the chemical stoichiometry of the sample after the RTA process by resulting in the addition of extra carriers in favor of superconductivity.