Measurement of energy gaps in superconductors by means of quantum interference devices

Abstract

The effect of temperature on the form of discrete changes in the current in highly inductive ($10 À6 H) doubly-connected superconductors with niobium-niobium clamped point contacts is determined experimentally. The magnitude and duration of the voltage pulse on a doubly-connected superconductor is measured at the time of the discrete change in its current state. The pulse magnitude is close to the energy gap 2D/e of the superconductor and its duration ($10 À6 s) corresponds to the minimum possible time ($10 À12 s) for a change in the state of the contact when the depairing current through it is reached. The measurement data are discussed in terms of models of the quantum interference of currents in a doubly-connected superconductor with clamped point contacts in the form of a quantum interferometer.

The effect of alternating current on the current states of a quantum interferometer shunted by a superconducting inductance

“…2(a)]. 8 The main electrical characteristics of the SQUID-SI structure include: the dependence of current (I 1 ) through a SI on the magnitude of direct transport current (I) through the SQUID 1,2 and the dependence of current I 1 on an external constant magnetic field (H) through the superconducting circuit with a SI at zero transport current (I = 0). A typical view of these dependencies is shown in Fig.…”

“…The SQUID-SI structure shown in Fig. 1 is in fact a large superconducting circuit, with one of its branches being an asymmetric two-contact SQUID with an extremely small inductance (L 0 ∼ 10 -13 H), 2,3 and the other being its part with a significantly greater inductance (L = 10 -6 H).…”

“…The structure of the SQUID-SI is formed in a manner similar to that described in our earlier works. [1][2][3] A PPC is one (k = 1) or several (k > 1) microcontacts in the place where the niobium microwires are pressed. The exact number depends on the surface structure of the microwire and the strength of its compression.…”

“…Shunting of a SQUID with a SI was proposed by us several years ago. [1][2][3][4] As shown in Refs. 2 and 3, the use of this structure makes it possible to simultaneously measure the energy gap and the relaxation time of the superconducting state in superconductors.…”

Thin film superconducting quantum interferometer with ultralow inductance

“…This structure consists of a high-inductance (circuit inductance greater 10 À9 H) superconducting circuit with an asymmetric SQI with two Josephson junctions in its gap. [4][5][6] Up to now we have used a niobium-niobium compression point contact (CPC) for an SQI of this type. Figure 1 shows a conceptual drawing of a doubly-connected structure with a CPC and its equivalent circuit.…”