Tunneling spectroscopy of $s\pi$ pairing state as a model for FeAs superconductors

We present the self-consistent Bogoliubov-de Gennes calculations of an $s\pi$ pairing state of two band superconductivity as a model for the FeAs superconductors. The $s\pi$ state is an s-wave pairing state with an internal $\pi$ phase, that is, nodeless gaps on each band but with the opposite sign. The novel features of this state are investigated by calculating the local density of states of the $\pi$ phase superconductor/normal metal bilayers. Because of the sign reversal between the two condensates, the zero bias conductance peak appears as observed in tunneling spectroscopy experiments on FeAs superconductors. This eliminates the major obstacle to establish the $s\pi$ state as the pairing symmetry of the FeAs superconductors.