The effect of varying Fe-content on transport properties of K intercalated iron selenide KxFe2-ySe2

TL;DR

This study investigates how varying iron content in KxFe2-ySe2 affects its transport properties, revealing a transition from insulating to superconducting states and suggesting vacancy ordering influences resistivity anomalies.

Contribution

It provides new insights into the role of iron vacancies in transport behavior and superconductivity in KxFe2-ySe2, including the highest Tc reported for iron selenides.

Findings

Superconductivity up to 44 K observed in some samples.

Resistivity shows a metallic behavior with minimal iron vacancies.

The 'hump' in resistivity is linked to vacancy ordering, not magnetic transition.

Abstract

We report the successful growth of high-quality single crystals of potassium intercalated iron selenide KxFe2-ySe2 by Bridgeman method. The effect of iron vacancies on transport properties was investigated by electrical resistivity and magnetic susceptibility measurements. With varying iron content, the system passes from semiconducting/insulating to superconducting state. Comparing with superconductivity, the anomalous "hump" effect in the normal state resistivity is much more sensitive to the iron deficiency. The electrical resistivity exhibits a perfect metallic behavior (R300K/R35K=42) for the sample with little iron vacancies. Our results suggest that the anomalous "hump" effect in the normal state resistivity may be due to the ordering process of the cation vacancies in this non-stoichiometric compound rather than magnetic/structure transition. A trace of superconductivity extending up to near 44 K was also detected in some crystals of KxFe2-ySe2, which has the highest Tc of the reported iron selenides.