Alternating-current properties of short Josephson weak links

Article

关键词: SUPERCONDUCTING QUANTUM POINT;    MAGNETIC-FIELD DEPENDENCE;    ORDER-PARAMETER;    TRANSPORT;    CONTACTS;    NOISE;    ALLOYS;    RELAXATION;    RESISTANCE;    EQUATIONS;   

DOI  :  10.1103/PhysRevB.95.134518

来源: SCIE

【 摘 要 】

We calculate the admittance of two types of Josephson weak links-the first is a one-dimensional superconducting wire with a local suppression of the order parameter, and the second is a short S-c-S structure, where S denotes a superconducting reservoir and c is a constriction. The systems of the first type are analyzed on the basis of time-dependent Ginzburg-Landau equations derived by Gor'kov and Eliashberg for gapless superconductors with paramagnetic impurities. It is shown that the impedance Z(Omega) has a maximum as a function of the frequency Omega, and the electric field E-Omega is determined by two gauge-invariant quantities. One of them is the condensate momentum Q(Omega) and another is a potential mu related to charge imbalance. The structures of the second type are studied on the basis of microscopic equations for quasiclassical Green's functions in the Keldysh technique. For short S-c-S contacts (the Thouless energy E-Th = D/ L-2 >> Delta), we present a formula for admittance Y valid frequencies Omega and temperatures T less than the Thouless energy E-Th (h Omega, T << E-Th) but arbitrary with respect to the energy gap Delta. It is shown that, at low temperatures, the absorption is absent [Re(Y) = 0] if the frequency does not exceed the energy gap in the center of the constriction (Omega < Delta cos phi(0), where 2 phi(0) is the phase difference between the S reservoirs). The absorption gradually increases with increasing the difference (Omega - Delta cos phi(0)) if 2 phi(0) is less than the phase difference 2 phi(c) corresponding to the critical Josephson current. In the interval 2 phi(c) < 2 phi(0) < pi, the absorption has a maximum. This interval of the phase difference is achievable in phase-biased Josephson junctions. Close to T-c the admittance has a maximum at low Omega, which is described by an analytical formula.

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