Effect of varying iron content on the transport properties of the potassium-intercalated iron selenide ${\mathrm{K}}_{x}$Fe${}_{2\ensuremath{-}y}$Se${}_{2}$

Effect of varying iron content on the transport properties of the potassium-intercalated iron selenide $K_{x}$ Fe $_{2 - y}$ Se $_{2}$

D. M. Wang, J. B. He, T.-L. Xia, and G. F. Chen

Phys. Rev. B 83, 132502 – Published 6 April 2011

Abstract

We report the successful growth of high-quality single crystals of potassium-intercalated iron selenide $K_{x}$ Fe $_{2 - y}$ Se $_{2}$ by the Bridgman method. The effect of iron vacancies on transport properties was investigated by electrical resistivity measurement. With varying iron content, the system passes from a semiconducting or insulating state to a superconducting state. Compared 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 ( $R_{300 K} / R_{35 K} \approx 42)$ 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 nonstoichiometric compound rather than to a magnetic or structure transition. A trace of superconductivity extending up to near 44 K was also detected in some crystals of $K_{x}$ Fe $_{2 - y}$ Se $_{2}$ , which has the highest $T_{c}$ of the reported iron selenides.