title: KFe2Se2 is the parent compound of K-doped iron selenide superconductors.
abstract: We elucidate the existing controversies in the newly discovered K-doped iron selenide (K(x)Fe(2-y)Se(2-z)) superconductors. The stoichiometric KFe(2)Se(2) with √2 × √2 charge ordering was identified as the parent compound of K(x)Fe(2-y)Se(2-z) superconductor using scanning tunneling microscopy and spectroscopy. The superconductivity is induced in KFe(2)Se(2) by either Se vacancies or interacting with the antiferromagnetic K(2)Fe(4)Se(5) compound. In total, four phases were found to exist in K(x)Fe(2-y)Se(2-z): parent compound KFe(2)Se(2), superconducting KFe(2)Se(2) with √2 × √5 charge ordering, superconducting KFe(2)Se(2-z) with Se vacancies, and insulating K(2)Fe(4)Se(5) with √5 × √5 Fe vacancy order. The phase separation takes place at the mesoscopic scale under standard molecular beam epitaxy conditions.
authors.affiliation: State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Hao
authors.initials: H
authors.lastname: Ding
authors.forename: Zhi
authors.initials: Z
authors.lastname: Li
authors.forename: Peng
authors.initials: P
authors.lastname: Deng
authors.forename: Kai
authors.initials: K
authors.lastname: Chang
authors.forename: Ke
authors.initials: K
authors.lastname: He
authors.forename: Shuaihua
authors.initials: S
authors.lastname: Ji
authors.forename: Lili
authors.initials: L
authors.lastname: Wang
authors.forename: Xucun
authors.initials: X
authors.lastname: Ma
authors.forename: Jiang-Ping
authors.initials: JP
authors.lastname: Hu
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.forename: Qi-Kun
authors.initials: QK
authors.lastname: Xue