Charge imbalance in non-equilibrium superconductors

A simple review is given of a number of phenomena in non-equilibrium superconductors which are usually described in terms of quasiparticle branch imbalance. It is shown how these may be described in terms of a two-component model for the charge, in which part of the charge is associated with the quasiparticles and the remainder with the superconducting electrons. This model is compared with the usual two-fluid model, and applications to situations of experimental interest, including tunnel injection experiments, the Carlson-Goldman collective mode, and quasiparticle diffusion near phaseslip centres are considered. In addition a number of thermoelectric phenomena are described, including generation of charge imbalance in a current-carrying superconductor in a temperature gradient. (author)