Spin-bottleneck due to spin-charge separation in a superconductor

Abstract

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 (Ni0.8Fe0.2) 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 quasiparticles and spin-bottleneck due to the enhanced recombination time of pure spin excitations. © 2005 The American Physical Society.