Superconductivity and Magnetism in (Tl, K, Rb)Fe_<i>x</i>Se₂

Abstract

The iron selenide superconductors AFexSe2 (A=Tl, K, Rb and Cs) discovered at the end of 2010 has attracted great interest because they display a variety of properties unprecedented for the cuprates and iron pnictides. Here, we present the motivation for our discovery on the superconductivity in (Tl,K,Rb)FexSe2 system, in which the onset superconducting transition temperature is as high as 40 K. We found that the compound with more Fe vacancies is an AFM insulator, which has been confirmed to be associated with the Fe-vacancy ordering in the crystals. Our discovery represents the first Fe-based superconductivity at the verge of an AFM insulator. A review on the recent results of Fe-vacancy super-lattice, AFM ordering, superconductivity and phase separation in (Tl,K,Rb)FexSe2 system is presented.