Coherent charge transport in metallic proximity structures

Golubov, A. A.; Wilhelm, Frank K.; Zaikin, Andrei D.

doi:10.1103/physrevb.55.1123

Cited by 120 publications

(198 citation statements)

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“…28 By applying the VZK theory, a number of authors investigated theoretically charge transport in various proximity structures. [28][29][30][31][32][33][34][35][36][37][38][39] This work was based on the boundary conditions for the KeldyshNambu Green's function at the DN/S interface derived by Kupriyanov and Lukichev ͑KL͒ 40 from Zaitsev's boundary condition 41 in the isotropic limit. The KL boundary conditions were recently extended by Nazarov within the circuit theory 42 and applied by Tanaka et al 43 to the study of charge transport in N/S junctions with arbitrary interface transparency in order to investigate more complex structures.…”

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confidence: 99%

Theory of thermal and charge transport in diffusive normal metal/superconductor junctions

et al. 2005

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Thermal and charge transport in diffusive normal metal ͑DN͒/insulator/s-, d-, and p-wave superconductor junctions are studied based on the Usadel equation with the Nazarov's generalized boundary condition. We derive a general expression of the thermal conductance in unconventional superconducting junctions. Thermal conductance, electric conductance of junctions and their Lorentz ratio are calculated as a function of resistance in DN, the Thouless energy, magnetic scattering rate in DN and transparency of the insulating barrier. We also discuss transport properties for various orientation angles between the normal to the interface and the crystal axis of superconductors. It is demonstrated that the proximity effect does not influence the thermal conductance while the midgap Andreev resonant states suppress it. Dependencies of the electrical and thermal conductance on temperature are sensitive to pairing symmetries and orientation angles. The results imply a possibility to distinguish one pairing symmetry from another based on the results of experimental observations.

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Section: Introductionmentioning

confidence: 99%

Theory of thermal and charge transport in diffusive normal metal/superconductor junctions

et al. 2005

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“…This achievement allowed us to observe for the first time a decrease in the differential resistance with pronounced double-dip structure within the superconducting energy gap and to measure the dependence of this structure on the magnetic field. Previously, experiments on transparent S/2DEG junctions (in diffusive limit) revealed a peculiar non-monotonic voltage dependence of the differential resistance with a maximum at zero bias, referred to as "reentrant" resistance [14,15,16,17,18].…”

Section: Introductionmentioning

confidence: 99%

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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“…The critical current is a thermodynamic property with contributions from quasiparticles within k B T of the Fermi energy, and decays within the coherence length. In contrast, the phase coherent conductance is a kinetic property with contributions within the Thouless energy E T h = hD/L 2 cd , and survives up to the order of L φ [7,14,15]. In this limit the Josephson circuit phase is given by…”

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Andreev Probe of Persistent Current States in Superconducting Quantum Circuits

et al. 2005

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Using the extraordinary sensitivity of Andreev interferometers to the superconducting phase difference associated with currents, we measure the persistent current quantum states in superconducting loops interrupted by Josephson junctions. Straightforward electrical resistance measurements of the interferometers give continuous read-out of the states, allowing us to construct the energy spectrum of the quantum circuit. The probe is estimated to be more precise and faster than previous methods, and can measure the local phase difference in a wide range of superconducting circuits.PACS numbers: 03.67. Lx, 85.25.Cp , 85.25.Dq Superconducting circuits consisting of loops interrupted by Josephson junctions show persistent current states that are promising for implementation in a quantum computer [1]. Spectroscopy and coherent quantum dynamics of the circuits have been successfully investigated by determining the switching-to-voltage-stateprobability of an attached superconducting quantum interference device (SQUID) [2]; however, a single switching measurement is low resolution and strongly disturbs both the circuit and the SQUID itself. This revives the fundamental problem of fast high resolution quantum measurements of the persistent current states. The conceptual and technological advance reported here is based on the fact that a persistent current in a quantum circuit is associated with the gradient of the superconducting phase χ of the macroscopic wavefunction describing the circuit. The problem of measuring the current reduces to a measurement of the corresponding phase difference θ q across the Josephson junctions.To measure θ q with a minimum of disruption we use an Andreev interferometer [3,4]. Our Andreev interferometers, shown in the scanning electron microscope images in Figs. 1a and b, are crossed normal (N ) silver conductors a-b and c-d, with contacts to a pair of superconducting (S) aluminium wires at the points c and d. The N/S interfaces play the role of mirrors reflecting electrons via an unusual mechanism first described by Andreev [5]. In Andreev reflection, an electron which is incident on the normal side of the N/S interface evolves into a hole, which retraces the electron trajectory on the N -side, and a Cooper pair is created on the S-side. There is a fundamental relationship between the macroscopic phase of the superconductors and the microscopic phase of the quasiparticles [6]: the hole gains an extra phase equal to the macroscopic phase χ, and correspondingly the electron acquires an extra phase −χ. This leads to phase-periodic oscillations in the resistance R A between the points a and b of the interferometer. It should be emphasized that the macroscopic phase is probed by quasiparticles with energies much less than the superconducting gap, so there is no "quasiparticle poisoning" of the superconductor.We investigate a Josephson quantum circuit with an attached Andreev interferometer, as shown in Figs. 1a and c. To probe the phase difference within the Josephson circuit, superconducting ...

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Coherent charge transport in metallic proximity structures

Cited by 120 publications

References 32 publications

Theory of thermal and charge transport in diffusive normal metal/superconductor junctions

Theory of thermal and charge transport in diffusive normal metal/superconductor junctions

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

Andreev Probe of Persistent Current States in Superconducting Quantum Circuits

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