Investigating microwave absorption in asymmetric Si quantum wells in an external magnetic
field, we discover a spin dependent component of Joule heating at spin resonance.
We explain this effect in terms of Rashba spin-orbit coupling which results in a current
induced spin precession and Zitterbewegung. Evidence is based on the observation of
a specific dependence of the electron spin resonance line shape and its amplitude
on the experimental geometry which in some range suggests a "negative" differential