Possibility of p-wave triplet pairing in Nb/Ni bilayers

We have experimentally investigated the density of states (DOS) in Nb/Ni (S/F) bilayers and found the anomalous double peak structure. In order to analyze the measured DOS data, we propose a theory model in which $p$-wave triplet pairing correlations are induced by an inhomogeneous magnetization in the ferromagnet. The induced triplet component penetrates into the ferromagnet over a long length (much larger than a characteristic length scale $\xi_F=\sqrt{D/h}$, where $D$ is the diffusion coefficient and $h$ exchange energy). We numerically calculate the DOS of Nb/Ni bilayers based on Eilenberger equation with various parameters and discuss the unusual sub-gap structure in the DOS. We find a good qualitative and quantitative agreement between the model calculations and our measurements and therefore suggest the possibility of $p$-wave triplet correlations in Nb/Ni bilayers.