Disordered Fe vacancies and superconductivity in potassium-intercalated iron selenide (K2-xFe4+ySe5)

TL;DR

This study identifies Fe-vacancy ordered K2Fe4Se5 as the magnetic parent compound of superconducting potassium-intercalated FeSe, showing that superconductivity arises from Fe-vacancy order-disorder transition, offering insights into iron-based superconductors.

Contribution

It unambiguously demonstrates that Fe-vacancy order in K2Fe4Se5 is the parent compound and that superconductivity emerges from vacancy disorder, clarifying the relationship between magnetism and superconductivity.

Findings

K2Fe4Se5 is the magnetic, Mott insulating parent compound.

Superconductivity appears after high-temperature annealing.

Superconductivity is linked to Fe-vacancy order-disorder transition.

Abstract

The parent compound of an unconventional superconductor must contain unusual correlated electronic and magnetic properties of its own. In the high-Tc potassium intercalated FeSe, there has been significant debate regarding what the exact parent compound is. Our studies unambiguously show that the Fe-vacancy ordered K2Fe4Se5 is the magnetic, Mott insulating parent compound of the superconducting state. Non-superconducting K2Fe4Se5 becomes a superconductor after high temperature annealing, and the overall picture indicates that superconductivity in K2-xFe4+ySe5 originates from the Fe-vacancy order to disorder transition. Thus, the long pending question whether magnetic and superconducting state are competing or cooperating for cuprate superconductors may also apply to the Fe-chalcogenide superconductors. It is believed that the iron selenides and related compounds will provide essential information to understand the origin of superconductivity in the iron-based superconductors, and possibly to the superconducting cuprates.