Tunnel injection and tunnel stimulation of superconductivity: The role of branch imbalance

The tunnel injection and the tunnel extraction of quasiparticles in a super conductor are considered, taking into account the branch population inbalance. The stability of nonequilibrium states with branch imbalance is discussed. It is shown that if this imbalance is large enough, the nonequilibrium state becomes unstable with respect to spatially homogeneous fluctuations of the order parameter, the characteristic increment being of the order of that for the Cooper instability of the normal state at T > T sub(c). As a result, states with oscillating order parameter can exist in a superconductor under injection or extraction. The relation of the results obtained to experimental results is discussed.