Scaling theory of conduction through a normal-superconductor microbridge

Beenakker, C. W. J.; Rejaei, B.; Melsen, J. A.

doi:10.1103/physrevlett.72.2470

Cited by 68 publications

(80 citation statements)

References 15 publications

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“…Properties of disordered contacts have been first studied theoretically by Artemenko, Volkov, and Zaitsev [46] and later in Refs. [15,16,17,18,22,23,24,25,26,27,28,29,30,31,32,33,34,35]. The transport measurements on the S/N structures in the diffusive limit have been carried out in [19,20,21] and have revealed a conductance peak around zero bias voltage which arises due to an interplay between Andreev scattering and disorder-induced scattering in the normal electrode.…”

Section: Discussion and Comparison With Theorymentioning

confidence: 99%

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Andreev reflection and enhanced subgap conductance in NbN∕Au∕InGaAs-InP junctions

Batov

Schaepers

Golubov

et al. 2004

Journal of Applied Physics

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We report on the fabrication of highly transparent superconductor/normal metal/twodimensional electron gas junctions formed by a superconducting NbN electrode, a thin (10nm) Au interlayer, and a two-dimensional electron gas in a InGaAs/InP heterostructure. High junction transparency has been achieved by exploiting of a newly developed process of Au/NbN evaporation and rapid annealing at 400 • C. This allowed us to observe for the first time a decrease in the differential resistance with pronounced double-dip structure within the superconducting energy gap in superconductor-2DEG proximity systems. The effect of a magnetic field perpendicular to the plane of the 2DEG on the differential resistance of the interface was studied. It has been found that the reduced subgap resistance remains in high magnetic fields. Zero-field data are analyzed within the previously established quasiclassical model for the proximity effect.

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Section: Discussion and Comparison With Theorymentioning

confidence: 99%

“…[22,23,24,25,26,27,28,29,30,31,32,33,34,35]. Below we will argue that the new double-dip structure in the differential resistance detected in our measurements is related to the transport in SN-2DEG contacts in a ballistic regime [1].…”

Section: Introductionmentioning

confidence: 98%

Andreev reflection and enhanced subgap conductance in NbN∕Au∕InGaAs-InP junctions

Batov

Schaepers

Golubov

et al. 2004

Journal of Applied Physics

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“…In this case, the current can be calculated within the mesoscopic approach, 12 by integrating over contributions of normal conducting eigenmodes with randomly distributed transparencies. The relevant distribution is known to be spread over the interval ∼ (L/ℓ)D ≫ D. 13 The most transparent modes dominate the subgap current, giving D eff ∼ (L/ℓ)D. In our case of junctions with large distance to the reservoirs, the scale of the spatial variation of the Green's function ξ 0 plays the role of the effective junction length giving qualitatively our result, D eff ∼ (ξ 0 /ℓ)D. 14 We note that for the long junctions under consideration the statistics of the eigenmode transparencies is not known, and a quantitative result has to be derived from the quasiclassical theory for diffusive superconductors.Our analysis is based on the diffusive equations 15 for the quasiclassical two-time Keldysh-Green functionsǦ(r r r,t 1 ,t 2 ), …”

mentioning

confidence: 99%

Subgap current in superconducting tunnel junctions with diffusive electrodes

et al. 2006

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We calculate the subgap current in planar superconducting tunnel junctions with thin-film diffusive leads. It is found that the subharmonic gap structure of the tunnel current scales with an effective tunneling transparency which may exceed the junction transparency by up to two orders of magnitude depending on the junction geometry and the ratio between the coherence length and the elastic scattering length. These results provide an alternative explanation of enhanced values of the subgap current in tunneling experiments often ascribed to imperfection of the insulating layer. We also discuss the effect of finite lifetime of quasiparticles as the possible origin of additional enhancement of multiparticle tunnel currents. PACS numbers: 74.45.+c, 74.40.+k, 74.25.Fy, 74.50.+r Subgap quasiparticle current in superconducting junctions at small applied voltages eV < 2∆ is the subject of persistent theoretical interest and experimental research. Recently, the problem has attracted new attention, and a number of measurements of the subgap current in high-quality tunnel junctions have been performed, 1,2 motivated by the problem of decoherence in Josephson-junction-based superconducting qubits. 3 The subgap current at zero temperature is due to multiparticle tunneling (MPT) processes, 4 whose intensities strongly depend on the quality of the insulating layer, being enhanced by disorder, localized electronic states, pinholes, etc. 5 The effect of disorder in the junction electrodes on the subgap current has never been questioned.According to the MPT theory, 4 the subgap tunnel current depends on the transparency D of the tunnel barrier: it decreases with decreasing voltage in a steplike fashion with step heights proportional to (D/2) n at voltages eV = 2∆/n, n = 1, 2... [subharmonic gap structure (SGS)]. Similar results have been obtained for junctions with ballistic electrodes, 6 and mesoscopic point contacts with diffusive electrodes 7 on the basis of the theory of multiple Andreev reflections (MAR). 5 Experimentally, the SGS scaling parameter in atomic size junctions nicely agrees with the theory; 8 however, in macroscopic tunnel junctions it is usually much larger 1,2 (see also earlier data 9 ); moreover, there is a smooth residual current at a very low voltage.1 Although enhanced SGS in hightransmission junctions could be explained by assuming randomly distributed resonant levels within the tunnel barrier, 10 enhanced subgap current in low-transmission junctions with presumably good insulating layers remains an open question.In this paper we reexamine the problem of the subgap current in macroscopic tunnel junctions, and consider the effects of diffusive electrodes and planar junction geometry common for the experiment (see Fig. 1). Our main result is that the SGS scaling parameter for such junctions significantly exceeds the junction transparency: for the sandwich-type junction with thin-film leads shown in Fig. 1(b), the scaling is determined by the effective transparency defined aswhere ξ 0 = D/2∆ is the diffus...

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“…In this case it is convenient to rewrite it in terms of the new variable t = R D /R T = aζ and the function U (x, t) = u(x, ζ)/a as U t + U U x = 0, with the initial condition U (x, 0) = sin x. In this representation, all information about geometry of the system had gone, and the Euler equation for U (x, t) describes evolution of {γ n } for any (not only 2D) system consisting of a tunnel barrier and a diffusive conductor in the zero-energy limit [23,26,12].…”

Section: Functional Rgmentioning

confidence: 99%

Proximity Action theory of superconductive nanostructures

2001

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We review a novel approach to the superconductive proximity effect in disordered normal-superconducting (N-S) structures. The method is based on the multicharge Keldysh action and is suitable for the treatment of interaction and fluctuation effects. As an application of the formalism, we study the subgap conductance and noise in two-dimensional N-S systems in the presence of the electron-electron interaction in the Cooper channel. It is shown that singular nature of the interaction correction at large scales leads to a nonmonotonuos temperature, voltage and magnetic field dependence of the Andreev conductance.

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Scaling theory of conduction through a normal-superconductor microbridge

Cited by 68 publications

References 15 publications

Andreev reflection and enhanced subgap conductance in NbN∕Au∕InGaAs-InP junctions

Andreev reflection and enhanced subgap conductance in NbN∕Au∕InGaAs-InP junctions

Subgap current in superconducting tunnel junctions with diffusive electrodes

Proximity Action theory of superconductive nanostructures

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