Sweeping this dependence by a low-frequency transport current (Fig.4b) allows us to observe, on the oscilloscope screen (Fig.4c), voltage pulses whose amplitude correspond to the niobium energy gap which turns out to be 2.3 mV at 4.2 К. Experimental values of the gap and calculated curve of temperature dependence of the gap are shown in Fig.5.
The duration of a quantum transition in the interferometer, i.e. the time of relaxation of superconducting state in niobium, can be estimated from ratio of inductance of the interferometer (L0 = 10-13 H) to that of the contour (L = 10-6 H):
τ ≈ (L0 / L) δt . (1)
Thus, as it follows from (1) at δt ≈ 10-5 s, τNb(4.2 K) ≈ 10-12 s. This value is close to Silver and Zimmerman's estimations [1