Self-blocking tunnel currents and current-voltage characteristics of S-I-S tunnel contacts

Nonequilibrium states in a superconductor are considered for quasiparticle injection at eV − 2Δ ≪ 2Δ, where eV is the voltage across the contact and Δ is the energy gap. It is shown that the excess of excitations over the equilibrium value (which are localized in the main above the gap) results in a self-blocking quasiparticle tunnel current. The relative magnitude of the effect is determined by the barrier transparency and also by the thickness of the films forming the tunnel contact, as well as by the potential difference. The nonequilibrium suppression of the superconducting gap on quasiparticle injection is considered for various limiting cases. The scope for determining Δ from tunnel experiments with homogeneous contacts is discussed.

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