Pure Spin Currents and the Associated Electrical Voltage

We present a generalized Landauer-Büttiker transport theory for multiterminal spin transport in the presence of spin-orbit interaction. Using this theory we point out that there exists equilibrium spin currents and nonequilibrium pure spin currents, without any magnetic element in the system. Quantitative results are presented for a $Y$-shaped conductor. It is shown that pure spin currents cause a voltage drop and, hence, can be measured.