Jun Zhao, Huibo Cao, E. Bourret-Courchesne, D. -H. Lee, R. J. Birgeneau
Identifying the parent compound and understanding its structural and magnetic properties have been proven to be very important in the study of high temperature (high-Tc) superconductors. For example, the parent compounds of the cuprates are antiferromagnetic (AF) Mott insulators while those of the iron pnictides are AF semi-metals [1, 2]. The recently discovered K-Fe-Se superconductor with coexisting sqrt5 *sqrt5 block AF order and superconductivity has caused heated debate in this regard [3-11]. Here we report neutron diffraction experiments which suggest that the parent compound of the K-Fe-Se superconductor is an AF semiconductor with a rhombus type iron vacancy order. Furthermore, the magnetic structure is the same as that in other iron pnictides and the Neel temperature is about 280 K. The superconductivity is induced by electron doping which completely suppresses the AF order. The fact that an antiferromagnetic semiconducting parent material can also lead to high-Tc superconductivity sets a new direction for the search for magnetic high-Tc superconductors.
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http://arxiv.org/abs/1205.5992
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