  Based on the spin-density-matrix approach, both the electric-field-induced
spin accumulation and the spin current are systematically studied for the
two-dimensional Rashba model. Eigenmodes of spin excitations give rise to
resonances in the frequency domain. Utilizing a general and physically
well-founded definition of the spin current, we obtain results that differ
remarkably from previous findings. It is shown that there is a close
relationship between the spin accumulation and the spin current, which is due
to the prescription of a quasi-chemical potential and which does not result
from a conservation law. Physical ambiguities are removed that plagued former
approaches with respect to a spin-Hall current that is independent of the
electric field. For the clean Rashba model, the intrinsic spin-Hall
conductivity exhibits a logarithmic divergency in the low-frequency regime.
