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 fluctuations. Two superconducting (SC) gap solutions are found to exist with the model: sign-changing s-wave gap (+/- s wave) and double d-wave gap states. Both solutions hold the approximate relation Delta(max)(h)N(h)approximate to Delta(max)(e)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.