Temperature dependence of the cosphi conductance in Josephson tunnel junctions determined from plasma resonance experiments

The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature Tc of the Sn films. The temperature dependence of the cosφ conductance is determined from the resonant response at the junction plasma frequency fp as the temperature is decreased from Tc.

We used three different schemes for observation of the plasma oscillations: (a) second-harmonic generation (excitation at ∼ 4.5 GHz, fp∼4.5 GHz); (b) mixing (excitations at ∼ 9 and ∼ 18 GHz, fp∼9 GHz); (c) parametric half-harmonic oscillation (excitation at ∼ 18 GHz, fp∼9 GHz). Measurements were possible in two temperature intervals, 0.994≤T / Tc≤0.982 and 0.965≥T / Tc≥0.930, with the result that as the temperature was decreased, the cosφ amplitude first increased from about zero to positive values and then at lower temperatures decreased approaching - 1 at the lowest temperatures of the experiment.