The electron pairing of K_xFe_2−ySe₂

¹ Department of Physics, Massachusetts Institute of Technology - Cambridge, MA 02139, USA
² Department of Physics, Beijing Institute of Technology - Beijing 100081, China
³ Department of Physics, Renmin University of China - Beijing 100872, China
⁴ Institute of Theoretical Physics, Chinese Academy of Sciences - Beijing 100190, China
⁵ Institute of Physics, Chinese Academy of Sciences - Beijing 100190, China
⁶ Department of Physics, University of California at Berkeley - Berkeley, CA 94720, USA
⁷ Materials Sciences Division, Lawrence Berkeley National Laboratory - Berkeley, CA 94720, USA

^a wangfa@mit.edu

Received: 1 February 2011
Accepted: 9 February 2011

Abstract

We studied the pairing instabilities in K_xFe_2−ySe₂ using a two-stage functional renormalization group (FRG) method. Our results suggest the leading and subleading pairing symmetries are nodeless d_x²−y² and nodal extended s, respectively. In addition, despite having no Fermi surfaces we find the buried hole bands make important contributions to the final effective interaction. From the bandstructure, spin susceptibility and the FRG results we conclude that the low-energy effective interaction in K_xFe_2−ySe₂ is well described by a J₁-J₂ model with dominant nearest-neighbor antiferromagnetic interaction J₁ (at least as far as the superconducting pairing is concerned). In the end we briefly mention several obvious experiments to test whether the pairing symmetry is indeed d_x²−y².