Intrinsic percolative superconductivity in K_xFe_2−ySe₂ single crystals

¹ Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences - P.O. Box 603, Beijing 100190, China
² Department of Physics, Renmin University of China - Beijing 100872, China
³ National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University Nanjing 210093, China

^a hhwen@nju.edu.cn

Received: 10 August 2011
Accepted: 14 September 2011

Abstract

Magnetic field penetration and magnetization hysteresis loops (MHLs) have been measured in K_xFe_2−ySe₂ single crystals. The magnetic field penetration shows a two-step feature with a very small full-magnetic-penetration field (≈300 Oe at 2 K), and accordingly the MHL exhibits an abnormal vanishing of the central peak near zero field below 13 K. The width of the MHL in K_xFe_2−ySe₂ at the same temperature is in general much smaller than that measured in Ba_0.6K_0.4Fe₂As₂ and Ba(Fe_0.92Co_0.08)₂As₂, and the MHLs in the latter two samples show a normal central peak near zero field. All these anomalies found in K_xFe_2−ySe₂ can be understood in the sense that the sample is percolative with weakly coupled superconducting islands.