Spin correlation function theory of spin-charge conversion effects

Theory of spin-charge conversion effects in spintronics are presented in terms of correlation functions of physical observables, spin and electric current. Direct and inverse spin Hall effects and spin pumping effect are studied considering metallic systems with random spin-orbit interaction and spatially nonuniform Rashba interaction. The theory is free from ambiguity associated with spin current, and provides clear physical picture of the spin-charge conversion effects. In the present approach, so-called the spin current transmission efficiency is essentially the nonuniform component of magnetic susceptibility.