  An experimental device was designed to measure the effect of the injection of
spin-polarized carriers on the superconductive gap and density-of-states (DOS).
Quasiparticles were injected from a ferromagnet ($Ni_{0.8}Fe_{0.2}$) through a
tunnel junction into a conventional superconductor (Nb), while charge
neutrality was maintained by a supercurrent. The DOS of the superconductor was
measured through a second tunnel junction with a normal paramagnetic metal. No
significant decrease of the superconductive gap was observed while a noticeable
heating of the quasiparticles of the superconductor was measured. A similar
experiment performed with current injected from a paramagnet (Al or Ag) showed
no heating of quasiparticles. These observations are consistent with
spin-charge separation of Bogoliubov quasi-particles and spin-bottleneck due to
the enhanced recombination time of pure spin-excitations.
