  The excitations in conventional superconductors, Bogoliubov quasiparticles,
are spin-1/2 fermions but their charge is energy-dependent and, in fact, zero
at the gap edge. Therefore, in superconductors (unlike normal metals) the spin
and charge degrees of freedom may be separated. In this article, we review spin
injection into conventional superconductors and focus on recent experiments on
mesoscopic superconductors. We show how quasiparticle spin transport and
out-of-equilibrium spin dependent superconductivity can be triggered using the
Zeeman splitting of the quasiparticle density of states in thin-film
superconductors with small spin-mixing scattering. Finally, we address the spin
dynamics and the feedback of quasiparticle spin imbalances on the strength of
the superconducting energy gap.
