  We discuss the Pauli Hamiltonian including the spin-orbit interaction within
an U(1) x SU(2) gauge theory interpretation, where the gauge symmetry appears
to be broken. This interpretation offers new insight into the problem of spin
currents in the condensed matter environment, and can be extended to Rashba and
Dresselhaus spin-orbit interactions. We present a few outcomes of the present
formulation: i) it automatically leads to zero spin conductivity, in contrast
to predictions of Gauge symmetric treatments, ii) a topological quantization
condition leading to voltage quantization follows, and iii) spin
interferometers can be conceived in which, starting from a arbitrary incoming
unpolarized spinor, it is always possible to construct a perfect spin filtering
condition.
