  Spin and charge transport through a quantum dot coupled to external
nonmagnetic leads is analyzed theoretically in terms of the non-equilibrium
Green function formalism based on the equation of motion method. The dot is
assumed to be subject to spin and charge bias, and the considerations are
focused on the Kondo effect in spin and charge transport. It is shown that the
differential spin conductance as a function of spin bias reveals a typical
zero-bias Kondo anomaly which becomes split when either magnetic field or
charge bias are applied. Significantly different behavior is found for mixed
charge/spin conductance. The influence of electron-phonon coupling in the dot
on tunneling current as well as on both spin and charge conductance is also
analyzed.
