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The energy gap (Δ) of a superconductor and the relaxation time (τ) of superconducting state are the key parameters of superconductors. The energy gap defines, in particular, the highest possible velocity of moving Cooper pairs and the critical current density of the superconductor. The relaxation time defines the maximum high-speed response of devices based on superconductors. Minimization of this parameter promotes development of high-frequency and weak-current superconducting devices for modern microwave and computer facilities.

We proposed and investigate now novel method which allows one to make simultaneous measurements of the gap and relaxation time. The method unites two base conceptions. The first of them is Silver and Zimmerman's theoretical prediction saying that the pulsed voltage *V*_{i} on superconducting quantum interferometer (SQI) during discrete switching of the circulating current *i* in it caused by variation of magnetic flux Ф_{x }is proportional to the energy gap of the superconductor (Fig.1). Second of them is our proposition of extending the pulse duration to a well-measurable value by shunting the interferometer with a superconducting coil with large inductance *L* ≈ *L*_{3} + *L*_{4} which considerably exceeds the inductance *L*_{0} of the interferometer (Fig.2).

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 (*L*_{0} = 10^{-13} H) to that of the contour (*L* = 10^{-6} H):

τ ≈ (*L*0 / *L*) δ*t . *(1)

Thus, as it follows from (1) at δ*t* ≈ 10^{-5} s, τ_{Nb}(4.2 K) ≈ 10^{-12} s. This value is close to Silver and Zimmerman's estimations [1].

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