Study of tunnel effects in Nb films with excess quasiparticles

Non-equilibrium state instability in superconducting Nb films is studied using broad (eV > 2δ) and narrow (δ >> eV-2δ) sources film-injected quasi-particles. Anomalous dependence of critical instability current Isub(n) on helium bath temperature is obtained for the broad source. Local heat build-up temperature Tsub(l) in the tunnel effect region is measured using pulse technique. Dependence of Isub(n) on local temperature Tsub(l) is not anomalous and is not contradictory to critical power temperature dependence #betta#sub(c)(T). In this case instability current diminishes with temperature decrease. It is in qualitative agreement with the superconductor threshold instability theory