Possible pairing states of the Fe-based superconductors

We consider the minimal two-band model for the Fe-based superconductors with a phenomenological pairing interaction which mimics short-range antiferromagnetic (AFM) fluctuations. Two superconducting (SC) gap solutions are found to exist with the model: sign-changing s-wave gap ($\pm$s-wave) and double d-wave gap states. Both solutions hold the approximate relation $\Delta_{h} ^{max} N_h \approx \Delta_{e} ^{max} N_e$, a generic feature of two band model with a dominant interband pairing interaction. We carried out the calculations of the SC properties of the both SC states such as the density of states, temperature dependencies of spin-lattice relaxation rate $1/T_1$, Knight shift, and penetration depth, particularly taking into account of the interband coherence factors. The results are discussed in comparison with the currently available experimental data.