title: Influence of microstructure on superconductivity in KxFe₂-ySe₂ and evidence for a new parent phase K₂Fe₇Se₈.
abstract: The search for new superconducting materials has been spurred on by the discovery of iron-based superconductors whose structure and composition is qualitatively different from the cuprates. The study of one such material, KxFe2-ySe2 with a critical temperature of 32 K, is made more difficult by the fact that it separates into two phases-a dominant antiferromagnetic insulating phase K2Fe4Se5, and a minority superconducting phase whose precise structure is as yet unclear. Here we perform electrical and magnetization measurements, scanning electron microscopy and microanalysis, X-ray diffraction and scanning tunnelling microscopy on KxFe2-ySe2 crystals prepared under different quenching processes to better understand the relationship between its microstructure and its superconducting phase. We identify a three-dimensional network of superconducting filaments within this material and present evidence to suggest that the superconducting phase consists of a single Fe vacancy for every eight Fe-sites arranged in a √8 x √10 parallelogram structure.
authors.affiliation: National Laboratory of Solid State Microstructures and Department of Physics, National Center of Microstructures and Quantum Manipulation, Nanjing University, Nanjing 210093, China.
authors.forename: Xiaxin
authors.initials: X
authors.lastname: Ding
authors.forename: Delong
authors.initials: D
authors.lastname: Fang
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Wang
authors.forename: Huan
authors.initials: H
authors.lastname: Yang
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Liu
authors.forename: Qiang
authors.initials: Q
authors.lastname: Deng
authors.forename: Guobin
authors.initials: G
authors.lastname: Ma
authors.forename: Chong
authors.initials: C
authors.lastname: Meng
authors.forename: Yuhui
authors.initials: Y
authors.lastname: Hu
authors.forename: Hai-Hu
authors.initials: HH
authors.lastname: Wen