Proximity-induced transport in hybrid mesoscopic normal–superconducting metal structures

Volkov, A. N.; Seviour, Rebecca; Павловский, В.

doi:10.1006/spmi.1999.0749

Cited by 11 publications

(11 citation statements)

References 47 publications

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“…However there is a formal analogy between these two cases because the formulae for the critical current can be reduced to each other by shifting the energy scale and by replacing h → eV (this analogy was noted in Refs. 26,27 ). In the case of a finite Q, the formulae forš become more complicated.…”

Section: S/f/s-junction With An Nonhomogeneous Magnetizationmentioning

confidence: 99%

Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization

2001

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We calculate the dc Josephson current IJ for two types of superconductor-ferromagnet (S/F) Josephson junctions. The junction of the first type is a S/F/S junction. On the basis of the Eilenberger equation, the Josephson current is calculated for an arbitrary impurity concentration. If hτ ≪ 1 the expression for the Josephson critical current Ic is reduced to that which can be obtained from the Usadel equation (h is the exchange energy, τ is the momentum relaxation time). In the opposite limit hτ ≫ 1 the superconducting condensate oscillates with period vF /h and penetrates into the F region over distances of the order of the mean free path l. For this kind of junctions we also calculate IJ in the case when the F layer presents a nonhomogeneous (spiral) magnetic structure with the period 2π/Q. It is shown that for not too low temperatures, the π-state which occurs in the case of a homogeneous magnetization (Q = 0) may disappear even at small values of Q. In this nonhomogeneous case, the superconducting condensate has a nonzero triplet component and can penetrate into the F layer over a long distance of the order of ξT = D/2πT . The junction of the second type consists of two S/F bilayers separated by a thin insulating film. It is shown that the critical Josephson current Ic depends on the relative orientation of the effective exchange field h of the bilayers. In the case of an antiparallel orientation, Ic increases with increasing h. We establish also that in the F film deposited on a superconductor, the Meissner current created by the internal magnetic field may be both diamagnetic or paramagnetic.

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Section: S/f/s-junction With An Nonhomogeneous Magnetizationmentioning

confidence: 99%

Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization

2001

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“…In diffusive 4-terminal S/N/S structures, the sign-reversal effect has been considered in Refs. [5][6][7] (see also [8,9]). The sign-reversal effect and switching of the π-junction into a state where ϕ = π has much in common with an instability of an uniform superconductor with a nonequilibrium distribution function [10,11].…”

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confidence: 99%

Suppression and enhancement of the critical current in multiterminal superconductor–normal-metal–superconductor mesoscopic structures

Seviour

Volkov

2000

Phys. Rev. B

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We analyse the measured critical current Im in a mesoscopic 4-terminal S/N/S structure. The current through the S/N interface is shown to consist not only of the Josephson component Ic sin ϕ, but also a phase-coherent part Isg cos ϕ of the subgap current. The current Im is determined by the both components Ic and Isg, and depends in a nonmonotonic way on the voltage V between superconductors and normal reservoirs reaching a maximum at V ∼ = ∆/e. The obtained theoretical resultas are in qualitative agreement with recent experimental data.Recent achievements in nanotechnology have revived interest in the study of nonequilibrium and phase-coherent phenomena in superconductor-normal metal (S/N) structures. One of the most remarkable, discovered recently [1], was the observation of the sign reversal of the Josephson critical current I c (the so-called π-junction) in a multiterminal mesoscopic Nb/Au/Nb structure under nonequilibrium conditions. By passing an additional current through the N layer or, in another words, by applying a voltage V to the normal reservoirs (see Fig.1) with respect to the superconductors, one can create a nonequlibrium electron-hole distribution, or at least one can shift this distribution with respect to the electron-hole distribution in the superconductors. Under this condition, the critical current I c decreases with V and changes sign at a certain value of the applied voltage V . This effect was predicted first in Ref.[2] where a ballistic 3-terminal structure was considered (for more details, see also Refs. [3,4]). In diffusive 4-terminal S/N/S structures, the sign-reversal effect has been considered in Refs. [5][6][7] (see also [8,9]). The sign-reversal effect and switching of the π-junction into a state where ϕ = π has much in common with an instability of an uniform superconductor with a nonequilibrium distribution function [10,11].In multi-terminal S/N/S structures one can observe not only the sign reversal effect, but also a number of other interesting phenomena. For example, the conductance of a normal wire between N reservoirs oscillates with varying phase difference ϕ (see review articles [12,13]). In addition, as shown in Refs. [5,14], the measured critical current I m depends on the geometry of a particular structure and instead of decreasing may also increase with increasing voltage V . In particular one can observe Josephson-like effects (plateau on the I 3 (V S ) curve, oscillations of the measured critical current I m in a magnetic field etc) even if the Josephson coupling between superconductors under equilibrium conditions is negligable. The reason for these effects is that the current I m in a multi-terminal S/N/S structure is determined not only by the Josephson component I c sin ϕ, but also by the phase-dependent subgap current I sg cos ϕ through the S/N interface. Therefore even in the case of a small I c , the current I m can be altered by varying the phase φ. An increase of the critical current was observed in the recent paper [15] where a mesoscopic three-terminal ...

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“…This is consistent with the assumption of a barrier resistance much higher than the diffusion resistance of the normal metal R T ӷR N . It also implies, that the proximity-enhanced diffusion conductivity, which is extensively discussed in recent literature, 14,15 gives an effect of the order of R N and can be neglected in this limit. The interplay of both phenomena in experimental setups will be discussed later on.…”

mentioning

confidence: 92%

“…14 and references therein ͑4-6, 49, and 50͒ as well as in Ref. 15. In this approach, the microscopic Gor'kov equation is reduced to the more handy Usadel equation by various systematic approximations.…”

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confidence: 99%

Mesoscopic proximity effect probed through superconducting tunneling contacts

Wilhelm

Golubov

2000

Phys. Rev. B

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We investigate the properties of complex mesoscopic superconducting-normal hybrid devices, Andreev Interferometers in the case where the current is probed through a superconducting tunneling contact whereas the proximity effect is generated by a transparent SN interface. We show within the quasiclassical Green'sfunctions technique, how the fundamental SNIS element of such structures can be mapped onto an effective SЈIS junction, where SЈ is the proximized material with an effective energy gap E g Ͻ⌬. The conductance through such a sample at Tϭ0 vanishes if VϽ⌬ϩE g , whereas at TϾ0 the conductance shows a peak at V ϭ⌬ϪE g . We propose the Andreev interferometer, where E g can be tuned by an external phase and displays maxima at 0 mod 2 and minima at mod 2. This leads to peculiar current-phase relations, which depart from a zero-phase maximum or minimum depending on the bias voltage and can even show intermediate extreme at VϷ⌬. We propose an experiment to verify our predictions and show how our results are consistent with recent, unexplained experimental results.The proximity effect, although already known for many decades ͑see, e.g., Ref. 1͒, has recently attracted renewed scientific interest in the context of mesoscopic normalsuperconducting hybrid structures, which are now experimentally acessible due to progress in nanofabrication and measurement support technology.2-4 Departing from the properties of single junction and the nonmonotonic diffusion conductance of SN wires, the interest turned to the possibility of tuning the conductance by an external phase or a loop in the normal part. On the other hand, if probed through tunneling contacts 5 the conductance is controlled by the DOS and the induced minigap, 6,7 which can also be controlled by a phase 8 and hence opens another channel for phase controlled conductance of a different sign.9,10 If a system contains more than one superconducting terminal, a supercurrent can flow. The situation becomes more difficult and, in particular, time dependent, if nonequilibrium is created by applying an external voltage parallel to the junction. This latter situation is substantially simplified, if one of the contacts is separated from the rest of the structure by a tunneling barrier. In that case, the voltage and phase drop is concentrated at the barrier and the problem is essentially split into two parts: The time dependence of the phase at the contact and the proximity effect, which determines the superconducting properties at the normal side of the contact, within the normal metal. In that case, the physics should be basically identical to the case of an SЈIS junction, where the properties of the ''superconductor'' SЈ are entirely controlled by the proximity effect, i.e., we expect a gap of size E g Ͻ⌬ where, if the junction is long, dӷ 0 E g ϰE Th ϭD/d 2 , the Thouless energy. Hence we will expect the known 11

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Proximity-induced transport in hybrid mesoscopic normal–superconducting metal structures

Cited by 11 publications

References 47 publications

Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization

Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization

Suppression and enhancement of the critical current in multiterminal superconductor–normal-metal–superconductor mesoscopic structures

Mesoscopic proximity effect probed through superconducting tunneling contacts

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