Showing papers by "Alexandre Avraamovitch Golubov published in 1996"
TL;DR: Nonstationary properties of ballistic constrictions SN/c/NS with disordered NS electrodes are analyzed theoretically and the appearance of series of subharmonic peaks associated with the two-gap structure in the density of states of NS electrodes is demonstrated.
Abstract: Nonstationary properties of ballistic constrictions SN/c/NS with disordered NS electrodes are analyzed theoretically. Amplitudes of Andreev and normal reflections at the constriction are related to the solutions of a stationary Green's function problem in an inhomogeneous NS electrode in the dirty limit. This provides a generalization of the model of Octavio, Tinhkam, Blonder, and Klapwijk for a spatially inhomogeneous case. The relation between the quasiparticle current in SN/c/NS junctions and the energy spectrum of a NS proximity sandwich is found for arbitrary parameters of N and S materials and of NS interfaces. The effect of the proximity layer on the excess current and the subharmonic structure are analyzed in detail and related to the parameters of the S and N materials. The appearance of series of subharmonic peaks associated with the two-gap structure in the density of states of NS electrodes is demonstrated. \textcopyright{} 1996 The American Physical Society.
75 citations
TL;DR: In this article, the authors analyzed the transport of charge carriers across PrBa2Cu3−xGaxO7−δ (PBCGO) barriers as a function of barrier thickness, Ga-doping level, temperature, and bias voltage.
Abstract: We analyzed the transport of charge carriers across PrBa2Cu3−xGaxO7−δ (PBCGO) barriers as a function of barrier thickness, Ga‐doping level, temperature, and bias voltage. It was found that by Ga doping, the normal state resistance (Rn) of the junctions was systematically increased, while the critical current (Ic) remained constant. We argue that pair transport takes place by direct tunneling, whereas the quasiparticles have access to channels formed by one or more localized states inside the barrier. By Ga doping the I cRn products were increased, up to 8mV at 4.2K for junctions with 8nm thick PrBa2Cu2.6Ga0.4O7−δ barriers.
67 citations
TL;DR: Two models that allow one to interpret the conductance mechanisms are presented and the parameters used in the models are within a realistic range given by characteristic material values.
Abstract: We have measured the differential resistance of lateral Nb contacts to a two-dimensional electron gas (2DEG) in an InP/${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructure. The I-V curves show strong deviations from the frequently used model developed by Blonder, Tinkham, and Klapwijk. In all samples the maximum of conductance at about eV=${\mathrm{\ensuremath{\Delta}}}_{0}$ is damped and shifted to lower voltages. Depending on the surface cleaning procedure two different regimes are observed. We will present two models that allow one to interpret the conductance mechanisms. The parameters used in the models are within a realistic range given by characteristic material values. In the case of wet chemically cleaned samples the 2DEG is assumed to be in the clean limit. To describe the measurement results of these samples we assume a proximity effect in a Nb oxide layer (N) located between the Nb (S) and the 2DEG causing the shift of the conductance maximum. Pair-breaking processes in this SN electrode are responsible for the damping of this maximum. Additionally we include the proximity effect between the electrode and the 2DEG in our model. When the semiconductor surface is cleaned by Ar ions, the 2DEG is damaged at the surface. For this case we have shown that an additional voltage drop occurs in this disturbed part of the 2DEG and that the inelastic scattering in the SN electrode is stronger than in the case of the wet chemically cleaned samples. \textcopyright{} 1996 The American Physical Society.
25 citations
TL;DR: In this article, nonstationary properties of ballistic constrictions NcN′S with disordered N'S electrodes are analyzed theoretically, and the relation between quasiparticle current in Nc N′S junctions and the energy spectrum of a n'S proximity sandwich is found for arbitrary parameters of N′ and S materials and of the interface.
Abstract: Nonstationary properties of ballistic constrictions NcN′S with disordered N'S electrodes are analyzed theoretically. Amplitudes of Andreev and normal reflections at the constriction are related to the solutions of a stationary Green's function problem in an inhomogeneous N′S electrode in a dirty limit. This provides a generalization of the model of Blonder, Tinkham and Klapwijk for a spatially inhomogeneous case. The relation between quasiparticle current in NcN′S junctions and the energy spectrum of a N'S proximity sandwich is found for arbitrary parameters of N′ and S materials and of the N′S interface.
14 citations
TL;DR: In this article, the microwave impedance of YBa 2 Cu 3 O 7-δ was measured using the hot finger cavity perturbation technique and compared with the isotropic s-wave BCS theory.
Abstract: Measurements of microwave impedance versus temperature, Z s (T), in Nb, Ba 0.6 K 0.4 BiO 3 , and YBa 2 Cu 3 O 7-δ are given. The measurements were made by the hot finger cavity perturbation technique. The electromagnetic properties of Nb are in a good quantitative agreement with the isotropic s-wave BCS theory. This model can also describe the experimental Z s (T) curves in Ba 0.6 K 0.4 BiO 3 crystals if the nonhomogeneous broadening of the superconducting transition is properly taken into account. The behavior of the microwave impedance of YBa 2 Cu 3 O 7-δ disagrees with the isotropic BCS theory. This suggests a strong anisotropy of the order parameter in this compound. Since the controversy between s- and d-wave descriptions of YBa 2 Cu 3 O 7-δ properties has not been resolved yet, we have checked a simpler strongly anisotropic s-wave model. Calculations by this model have been compared to measurements on YBa 2 Cu 3 O 7-δ . With due account of the strong-coupling effects, two-band anisotropy, and impurity scattering in YBa 2 Cu 3 O 7-δ , the agreement between the generalized BCS model and experimental data is surprisingly good.
12 citations
TL;DR: In this article, the core structure of the Abrikosov vortex perpendicular to the layers of a proximity effect SN multilayer is discussed, where the superconducting correlations are induced in N via the proximity effect and dirty limit conditions are fulfilled.
Abstract: The core structure of the Abrikosov vortex perpendicular to the layers of a proximity effect SN multilayer is discussed. We assume that the superconducting correlations are induced in N via the proximity effect and the dirty limit conditions are fulfilled. The approach for calculation of the local densities of states in N and S layers is developed in the framework of the quasiclassical Usadel equations. For the practically interesting case of SN bilayer, relevant to the STM spectroscopy, the densities of states and apparent STM vortex-core radius, related to the energy-dependent coherence length in N, are calculated.
5 citations
TL;DR: In this paper, the magnetic field strongly influences the effective conductance of weakly transparent contacts in InGaAs heterostructures, and it is explained in terms of a confinement of electron trajectories near the interface.
Abstract: Lateral Nb contacts to a high-mobility two-dimensional electron gas (2DEG) in InGaAs heterostructures are studied. Below T c of Nb a pronounced non-linearity due to the superconducting energy gap is observed in the differential resistance. The Nb/2DEG interface reveals an enhanced zero-bias resistance. In normal state, a drastic decrease of the resistance with increasing magnetic field perpendicular to the plane of the structure is observed. It is explained in terms of a confinement of electron trajectories near the interface with increasing magnetic field yielding an enhanced number of transmitted carriers. The suggested model shows good agreement with experiment. We conclude that the magnetic field strongly influences the effective conductance of weakly transparent contacts.
4 citations
01 Jan 1996
Abstract: Josephson and quasiparticle currents in SNcNS contacts are calculated for the regimes of ballistic constriction “c”. The relation between the current and electronic densities of states in NS proximity bilayer is found. The effect of the proximity N layer on the Andreev and normal reflections of electrons at the constriction is studied. Excess current at large voltages and subharmonic structure at low bias are analyzed as a function of material parameters of N and S and transparency of the NS interface. The appearance of new series of subharmonic peaks due to two-gap structure in the density of states of proximity NS electrodes is demonstrated. The relation between excess and critical currents is analyzed. The model is relevant for SNS junctions of constricted geometry which is realized in S-2DEG-S and step-edge highTc SNS contacts.
2 citations
TL;DR: In this article, the effect of the proximity N layer on the Andreev and normal reflections of electrons at the constriction is studied, and the relation between excess and critical currents is analyzed.
Abstract: Josephson and quasiparticle currents in SNcNS contacts are calculated for the regimes of ballistic constriction “c”. The relation between the current and electronic densities of states in NS proximity bilayer is found. The effect of the proximity N layer on the Andreev and normal reflections of electrons at the constriction is studied. Excess current at large voltages and subharmonic structure at low bias are analyzed as a function of material parameters of N and S and transparency of the NS interface. The appearance of new series of subharmonic peaks due to two-gap structure in the density of states of proximity NS electrodes is demonstrated. The relation between excess and critical currents is analyzed. The model is relevant for SNS junctions of constricted geometry which is realized in S-2DEG-S and step-edge highTc SNS contacts.
2 citations
01 Jan 1996
TL;DR: In this article, the authors generalized the approach developed by Blonder, Tinkham and Klapwijk (BTK) for calculation of the quasiparticle (qp) current in NcS contacts to the case of ScNS and SNcNS contacts with disordered NS electrodes.
Abstract: The approach developed by Blonder, Tinkham and Klapwijk (BTK) for calculation of the quasiparticle (qp) current in NcS contacts is generalized to the case of ScNS and SNcNS contacts with disordered NS electrodes. Amplitudes of Andreev and normal reflections at the ballistic constriction are calculated. The relation between the qp current and energy spectrum of NS proximity sandwich is found for arbitrary transparencies of the constriction and NS interfaces. The appearance of new series of subharmonic peaks associated with the two-gap structure in the density of states of NS electrodes is demonstrated. The model is also applied to calculation of the critical and the excess currents in ScNS and SNcNS for different interface parameters. The relevance of the model to transport mechanisms in step-edge HTS SNS contacts is discussed.
1 citations
TL;DR: In this paper, the authors studied the proximity effect in superconductor/ferromagnet multilayers by systematically varying the magnetic moment, which influences the superconductivity via the coherence length in the ferromagnetic layer.
Abstract: We have studied the proximity effect in superconductor/ferromagnet multilayers by systematically varying the magnetic moment, which influences the superconductivity via the coherence length in the ferromagnetic layer. We show that also the interface transparency has to be taken into account in such proximity systems. This interface transparency is found to depend on the magnetic moment.
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TL;DR: In this article, the authors developed a detailed analysis of electron transport in normal diffusive conductors in the presence of proximity induced superconducting correlation and calculated the linear conductance of the system and the profile of the electric field.
Abstract: We develop a detailed analysis of electron transport in normal diffusive conductors in the presence of proximity induced superconducting correlation. We calculated the linear conductance of the system and the profile of the electric field. A rich structure of temperature dependences was found and explained. Our results are consistent with recent experimental findings.
TL;DR: In this paper, the I-U characteristics of the different contact configurations are compared and discussed in terms of the interplay between Andreev and ordinary reflection processes at both kinds of Nb-2DEG interfaces.
Abstract: Lateral contacts between a high-mobility 2-dimensional electron gas (2DEG) and superconducting Nb have been prepared by etching down the heterostructure and depositing Nb on the mesa from the side. A second kind of contact has been achieved by depositing the Nb on top of the heterostructure contacting the 2DEG through a 60 nm thick barrier of Ga0.47In0.53As. Both kinds of contacts show a pronounced nonlinearity in the differential resistance due to the superconducting energy gap. The I-U characteristics of the different contact configurations are compared and discussed in terms of the interplay between Andreev and ordinary reflection processes at both kinds of Nb-2DEG interfaces.