Understanding spin Hall effects from the motion in SU(2)XU(1) fields

We derive the classical counterpart of a previously obtained quantum mechanical covariant ``continuitylike'' equation for the spin density, and present an intuitive picture for elucidating the non-conservation of the spin current. This reveals the equations of motion for a particle with spin under the Yang-Mills field (in certain semiconductors) as well as the Maxwell field, from which the condition for an infinite spin relaxation time is drawn out directly. As a concrete example, we discuss the procession of the spin orientation in spin Hall effect with the so called ReD field, which undergoes a circle with the frequency dependent on both the strength of the spin-orbit coupling and the initial velocity. The anti-commutation of the Pauli matrices is found to be crucial in simplifying the equations of motion in the view of quantum mechanism of the same topics.