Publication Type
Journal
Journal Name
Physical Review Letters
Publication Date
Page Number
217002
Volume
106
Issue
21
Abstract
We introduce and study an extended ‘‘t-U-J’’ two-orbital model for the pnictides that includes Heisenberg terms deduced from the strong coupling expansion. Including these J terms explicitly allows us to enhance the strength of the ð%;0Þ-ð0;%Þ spin order which favors the presence of tightly bound pairing states even in the small clusters that are here exactly diagonalized. The A1g and B2g pairing symmetries are found to compete in the realistic spin-ordered and metallic regime. The dynamical pairing susceptibility additionally unveils low-lying B1g states, suggesting that small changes in parameters may render any of the three channels stable.
