Functional integration method in the theory of superconductivity

Svidzinskii, A. V.

doi:10.1007/bf01036950

Cited by 16 publications

(16 citation statements)

References 12 publications

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“…Here, only the simplest conditions will be assumed, when (2) applies to a wide range of values of g ℓ and g δ . This agrees with the microscopic model results 16,19,20,[26][27][28][29] and, for instance, takes place within the GL approach for sufficiently large values of g ℓ and g δ , which is the particular focus of this paper.…”

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confidence: 78%

Anharmonic Josephson current in junctions with an interface pair breaking

Barash

2012

Phys. Rev. B

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Planar superconducting junctions with a large effective Josephson coupling constant and a pronounced interface pair breaking are shown to represent weak links with small critical currents and strongly anharmonic current-phase relations. The supercurrent near Tc is described taking into account the interface pair breaking as well as the current depairing and the Josephson coupling-induced pair breaking of arbitrary strengths. A new analytical expression for the anharmonic supercurrent, which is in excellent agreement with the numerical data presented, is obtained. In junctions with a large effective Josephson coupling constant and a pronounced interface pair breaking, the currentinduced depairing is substantially enhanced in the vicinity of the interface thus having a crucial influence on the current-phase relation despite a small depairing in the bulk. The Josephson current is one of the remarkable manifestations of quantum coherence on the macroscopic scale in condensed matter physics. The supercurrent depends on the phase difference of the order parameters across the junction interface. The study of the current-phase relation (CPR) in the junctions makes it possible to identify physical processes, which form supercurrents under diverse conditions. It is also beneficial for junction applications. The problem attracted much attention while studying both highly transparent junctions with strongly anharmonic CPRs and tunnel junctions, where the second harmonic of the supercurrent comes into play due to the suppression of the first one 1-10 . The latter takes place in the junctions involving unconventional superconductors with special interface-to-crystal orientations and at 0-π transitions.One of the earlier theoretical results, clarifying a variety of aspects of the problem, is the anharmonic CPR for the superconducting point contacts [11][12][13][14][15] . Due to the negligibly small current-induced pair breaking at any transparency value, the theory of point contacts is simplified. The depairing plays an important role in forming anharmonic CPRs in highly transparent planar junctions, unlike its negligible role in point contacts. Since the critical current j c of usual planar junctions becomes, with increasing transparency, comparable with the depairing current j dp in the bulk, the junctions do not represent weak links. In other words, in the junctions, the current-induced depairing brings about a pronounced anharmonicity only in the crossover from the tunnel Josephson current to the bulk superflow 1,16-18 .There are at least three types of pair breaking processes taking place in charge transport in the superconducting junctions: the pair breaking produced by the phase-dependent Josephson coupling, by the current and by the interface itself. These are the very same effects which can lead to a noticeably anharmonic CPR not only at low or intermediate temperatures, but also near T c . Here, I show that planar junctions with a large effective Josephson coupling constant and a pronounced interface pair breaking ca...

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confidence: 78%

Anharmonic Josephson current in junctions with an interface pair breaking

Barash

2012

Phys. Rev. B

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“…while in a strongly asymmetric case D D 1 2 << we again arrive at the expression (24). This implies that at resonance the barrier with higher transmission D 2 becomes effectively transparent even if D 2 1 << .…”

Section: Sini S ¢ Junctions With Few Conducting Channelssupporting

confidence: 63%

“…For instance, SNS systems with one insulating barrier, such as SINS and SNINS were analyzed by a number of authors [22][23][24][25][26][27][28]. For an extended review summarizing various features of dc Josephson effect in different types of superconducting weak links and further references we refer the reader to Refs.…”

Section: Instead Of Introductionmentioning

confidence: 99%

Some novel effects in superconducting nanojunctions

Zaikin

2004

Low Temperature Physics

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In this paper we address several new developments in the theory of dc Josephson effect in superconducting weak links. We analyze an interplay between quantum interference effects and Andreev reflection in SNS nanojunctions with insulating barriers and demonstrate that these effects may qualitatively modify the Josephson current in such structures. We also investigate an impact of the parity effect on persistent currents in superconducting nanorings interrupted by a quantum point contact (QPC). In the limit of zero temperature and for the odd number of electrons in the ring we predict complete suppression of the supercurrent across QPC with one conducting mode. In nanorings with SNS junctions a p-state can occur for the odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux. where f is the difference between the phases of the BCS order parameters of two superconductors. Equation (1) represents the dc Josephson effect. The answer to the Einstein's question [1] turned out to be positive.What if the total current I flowing through the barrier is larger than I c ? In this case a part of the net current across the barrier is transferred by normal electrons (quasiparticles) and the rest of it is carried by Cooper pairs. While the second contribution, I s , remains dissipativeless and is again described by Eq. (1), the first -quasiparticle -contribution to the current is dissipative and, hence, causes a nonzero voltage drop V across the insulating barrier. In the presence of this voltage the coherent phase difference f acquires a time dependence described by another famous Josephson relation ¶fCombining Eqs. (1) and (2) one immediately arrives at the conclusion that for any nonzero V the supercurrent I s changes in time. In the case of time-independent voltages one has f = 2eVt/h and, hence, the Josephson current (1) will oscillate in time with the fundamental frequency proportional to the voltage V. Equation (2) and related to it oscillations of the supercurrent represent the essence of the ac Josephson effect. Soon after these Josephson's predictions the microscopic theory of both dc [3] and ac [4,5] was constructed and these effects have been observed experimentally [6,7]. Huge number of publications as well as several monographs are devoted to various aspects of these effects. It turned out that physics encoded in these phenomena is very rich and important for understanding of basic properties of superconductivity it-

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“…In particular, the central Fraunhofer peak in clean planar and long SNS junctions with fully transparent interfaces has been found to get strongly distorted at low temperatures. At T = 0 it acquires a triangular form 11,12 , which correlates with a saw-toothed current-phase relation taking place under the same conditions in the systems 12,20 . This example demonstrates that pronounced anharmonic currentphase relations in superconducting junctions can entail significant qualitative modifications in the corresponding magnetic interference patterns.…”

Section: Introductionmentioning

confidence: 99%

“…Nonetheless, there are important plane contacts, where the physics of weak links is still valid even in the presence of highly transparent transport channels. This is the case for long superconductor-normal metal-superconductor (SNS) fully transparent junctions of various geometries, where interference patterns have been studied in detail theoretically at arbitrary temperatures and beyond the tunneling approximation [11][12][13][14][15][16][17][18][19] . In particular, the central Fraunhofer peak in clean planar and long SNS junctions with fully transparent interfaces has been found to get strongly distorted at low temperatures.…”

Section: Introductionmentioning

confidence: 99%

Magnetic interference patterns in superconducting junctions: Effects of anharmonic current-phase relations

Barash

2010

EPL

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A microscopic theory of the magnetic-field modulation of critical currents is developed for plane Josephson junctions with anharmonic current-phase relations. The results obtained allow examining temperature-dependent deviations of the modulation from the conventional interference pattern. For tunneling through localized states in symmetric short junctions with a pronounced anharmonic behavior, the deviations are obtained and shown to depend on distribution of channel transparencies. For constant transparency the deviations vanish not only near Tc, but also at T = 0. If Dorokhov bimodal distribution for transparency eigenvalues holds, the averaged deviation increases with decreasing temperature and takes its maximum at T = 0.

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Functional integration method in the theory of superconductivity

Cited by 16 publications

References 12 publications

Anharmonic Josephson current in junctions with an interface pair breaking

Anharmonic Josephson current in junctions with an interface pair breaking

Some novel effects in superconducting nanojunctions

Magnetic interference patterns in superconducting junctions: Effects of anharmonic current-phase relations

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