Fe-based superconductivity with T_c = 31 K bordering an antiferromagnetic insulator in (TI,K) Fe_xSe₂

¹ Department of Physics, Zhejiang University - Hangzhou 310027, China
² Department of Physics, Hangzhou Normal University - Hangzhou 310036, China

^a mhfang@zju.edu.cn

Received: 17 February 2011
Accepted: 21 March 2011

Abstract

(Tl,K)Fe_xSe₂ single crystals were first successfully synthesized with the Bridgeman method. The physical properties are characterized by electrical resistivity, magnetic susceptibility and Hall coefficient. We found that the (Tl,K)Fe_xSe₂ (1.30 ≤ x ≤ 1.65) compounds show an antiferromagetic (AFM) insulator behavior, which may be associated with the Fe-vacancy ordering in the crystals. While in the 1.70 ≤ x < 1.78 crystals, superconductivity (SC) coexists with an insulating phase. As Fe content further increases, the bulk SC with T_c = 31 K (and a T_c^onset as high as 40 K) appears in the 1.78 ≤ x ≤ 1.88 crystals. Our discovery represents the first Fe-based high-temperature superconductivity (HTSC) at the verge of an AFM insulator.