Spin-flip effects on Andreev reflection process

We investigate the nonequilibrium transport properties of a quantum dot in the normal-metal and superconductor hybrid system, where the Andreev reflection plays the important role. The electron spin-flip effect in quantum dot is explicitly taken into account. By using the nonequilibrium Green's function (NEGF) approach, we first give a general current formula which is valid for any bias and temperature, then we discuss the linear conductance in terms of the local density of states. The various resonant peaks appear for the different spin-flip strengths in quantum dot. Finally, we numerically calculate the current-bias characteristic when the bias is smaller than the superconductor gap.