Spin alignment induced by spin-orbit coupling in quantum plasmas

We develop a quantum hydrodynamic fluid model including spin-orbit coupling effects for electrons in quantum plasmas. An effective field being analogous to the magnetic field of the magnetic moment is found. In the strong-radiation case, this effective field has a more important influence on the motion of plasmas than the usual Bohm potential correction. We find a resonance-like mechanism by which the transverse electromagnetic (TEM) wave and the Langmuir wave both propagating in plasmas with the same frequency can cause a stationary alignment of spins. This alignment will become a traveling wave when the frequency increases. Then it will vanish when the reciprocal of the difference between the frequencies of TEM and Langmuir waves reaches a value shorter than the characteristic spin relaxation time.