  Spin accumulation is a crucial but imprecise concept in spintronics. In
metal-based spintronics it is characterized in terms of semiclassical
distribution functions. In semiconductors with a strong spin-orbit coupling the
spin accumulation is interpreted as a superposition of coherent eigenstates.
Both views can be reconciled by taking into account the electron-electron
interaction: a sufficiently strong self-consistent exchange field reduces a
spin accumulation to a chemical potential difference between the two spin bands
even in the presence of spin-orbit coupling. We demonstrate the idea on a clean
two-dimensional electron gas (2DEG) by showing how the exchange field protects
a spin accumulation from dephasing and introduces an easy-plane anisotropy.
