Mg coating induced superconductivity in the FeSe ultrathin film

TL;DR

This study demonstrates that simple Mg coating can induce superconductivity in non-superconducting FeSe ultrathin films by filling Fe vacancies and doping electrons, with optimal Mg levels enhancing superconductivity.

Contribution

It reveals a novel method of inducing superconductivity in FeSe films through Mg coating, highlighting vacancy filling and electron doping as key mechanisms.

Findings

Mg coating converts insulator to superconductor in FeSe ultrathin films.

Optimal Mg levels enhance superconducting properties.

Excess Mg degrades superconductivity due to electron concentration decrease.

Abstract

The transition from insulator to superconductor was achieved in the non-superconducting FeSe ultrathin film via simple Mg coating technique in present work. It was found that in non-superconducting FeSe ultrathin film without Mg coating, insulating \b{eta}-Fe1-xSe phase with iron-vacancy disorders is the main phase and more likely to be the parent phase of FeSe superconducting system. Proper Mg coating on the surface of FeSe films can lead to Mg entering FeSe crystal lattice to fill up these Fe vacancies rather than replace Fe. Simultaneously, additional electron doping is introduced and the electron carrier concentration in this parent phase can be tuned, which is responsible for the SIT and evolution of superconductivity in this system. However, abnormal decrease of electron concentration was found in FeSe film with excessive Mg coating, which brings about the severe degradation in superconducting performance.