Pure spin currents and associated electrical voltage

We present a generalize Landauer-B\"uttiker transport theory for multi-terminal spin transport in presence of spin-orbit interaction. It is pointed out that the presence of spin-orbit interaction results in {\it equilibrium spin currents}, since in presence of spin-orbit interaction spin is not a conserved quantitative. Further we illustrate the theory by applying it to a three terminal Y-shaped conductor. It is shown that when one of the terminal is a potential probe, there exist {\it nonequilibrium pure spin currents} without a n accompanying charge current. It is shown that this pure spin currents causes a voltage drop which can be measured if the potential probe is ferromagnetic.