Nonequilibrium ac Josephson Effect in Mesoscopic Nb-InAs-Nb Junctions

Lehnert, K. W.; Argaman, Nathan; Blank, H.-R.; Wong, K. C.; Allen, S. J.; Hu, Evelyn L.; Kroemer, H.

doi:10.1103/physrevlett.82.1265

Cited by 40 publications

(35 citation statements)

References 13 publications

(21 reference statements)

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“…Such a problem indeed reminds the one considered in Refs. [25,33,34]. In a clean SNS junction polarized with a voltage V , oscillations with a frequency double of the basic Josephson frequency ω = 2eV h are generated and show up under microwave irradiation as halfinteger Shapiro steps.…”

Section: B Resultsmentioning

confidence: 99%

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Subgap structure in the conductance of a three-terminal Josephson junction

et al. 2014

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Three-terminal superconductor (S) -normal metal (N) -superconductor (S) Josephson junctions are investigated. In a geometry where a T-shape normal metal is connected to three superconducting reservoirs, new sub-gap structures appear in the differential resistance for specific combinations of the superconductor chemical potentials. Those correspond to a correlated motion of Cooper pairs within the device that persist well above the Thouless energy and is consistent with the prediction of quartets formed by two entangled Cooper pairs. A simplified nonequilibrium Keldysh Green's function calculation is presented that supports this interpretation.

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Section: B Resultsmentioning

confidence: 99%

“…[25,33,34], e.g. that the voltage is small enough to allow an adiabatic approximation both in the current components and in the Andreev state distribution.…”

Section: B Resultsmentioning

confidence: 99%

Subgap structure in the conductance of a three-terminal Josephson junction

et al. 2014

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“…We have shown that the microscopic theory of coherent multiple Andreev reflections provides an unified description of Shapiro steps and assisted tunneling, explaining in a natural way the observations of subharmonic steps [14][15][16][17] and the peculiar subharmonic gap structure under a microwave radiation [10]. Let us finally remark that the results presented in this work are amenable to a quantitative experimental test using atomic-size contacts [2][3][4][5].…”

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confidence: 93%

“…Early experiments on the ac Josephson effect in weak links observed subharmonic steps in the I-V curves [14]. More recently, there have been reported observations of non-integer Shapiro steps in high-T C contacts [15], S-semiconductor-S junctions [16] and diffusive S-N-S systems [17]. Although the Shapiro steps can be understood as a simple consequence of a non-sinusoidal current-phase relation, the present approach goes beyond a simple "adiabatic" approximation and provides the first microscopic theory of Shapiro steps in contacts of arbitrary transmission.…”

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confidence: 99%

Subharmonic Shapiro Steps and Assisted Tunneling in Superconducting Point Contacts

et al. 2002

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We analyze the current in a superconducting point contact of arbitrary transmission in the presence of a microwave radiation. The interplay between the ac Josephson current and the microwave signal gives rise to Shapiro steps at voltages V = (m/n)hωr/2e, where n, m are integer numbers and ωr is the radiation frequency. The subharmonic steps (n = 1) are a consequence of multiple Andreev reflections (MAR) and provide a signature of the peculiar ac Josephson effect at high transmission. Moreover, the dc current exhibits a rich subgap structure due to photon-assisted MARs.Introduction.-Our understanding of the electronic transport through superconducting nanostructures has experienced a notable development in last few years [1]. Partly, this has been due to the appearance on scene of the metallic atomic-size contacts, which can be produced by means of scanning tunneling microscope and breakjunction techniques [2][3][4][5]. These nanowires have turned out to be ideal systems to test the modern transport theories in mesoscopic superconductors. Thus, for instance Scheer and coworkers [3] found a quantitative agreement between the measurements of the current-voltage characteristics of different atomic contacts and the predictions of the theory for a single-channel superconducting contact [6,7]. These experiments not only helped to clarify the structure of the subgap current in superconducting contacts, but also showed that the set of the transmission coefficients in an atomic-size contact is amenable to measurement. This possibility has recently allowed a set of experiments that confirm the theoretical predictions for transport properties like supercurrent [4] and noise [5]. From these combined theoretical and experimental efforts a coherent picture of transport in superconducting point contacts has emerged with multiple Andreev reflections (MAR) [8] as a central concept. However, in spite of these recent successes, one of the most remarkable predictions of MAR theory remains to be confirmed, namely the ac Josephson effect. The theory says that in a constant voltage biased superconducting point contact, the time-dependent current is given by I(t) = n I n e inω0t . This means that the occurrence of MARs gives rise to the appearance of alternating currents that oscillate not only with the Josephson frequency ω 0 = 2eV /h, V being the voltage, as in the case of tunnel junctions, but also with all its harmonics. So far there is no experimental evidence of the existence of such components.In this paper, we present a theoretical analysis of the current in a superconducting point contact under a microwave radiation. We show that the interplay between the ac Josephson current components and a microwave signal leads to the appearance of Shapiro steps at voltages V = (m/n)hω r /2e, where n, m are integer numbers and ω r is the frequency of the radiation. This means that in

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“…(8) in the case of a contact between a d-wave superconductor and a diffusive normal wire were derived in Ref. [16].…”

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confidence: 99%

Conductance ofd-Wave Superconductor/Normal Metal/d-Wave Superconductor Junctions

Pesin

Andreev²,

Spivak³

2008

Phys. Rev. Lett.

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We develop a theory of the conductance of superconductor/normal metal/superconductor junctions in the case where the superconducting order parameter has d-wave symmetry. At low temperature the conductance is proportional to the square root of the inelastic electron relaxation time in the bulk of the superconductor. As a result it turns out to be much larger than the conductance of the normal part of the junction.PACS numbers: 74.45.+c, 74.50.+r, 74.20.Rp At small voltages V , the current I through a superconductor/normal metal/superconductor (SNS) junction can be written asHere φ is the phase difference between the superconductors, and J(φ) is a periodic function of φ with period 2π. The time dependence of φ is given by the Josephson relation:The first term in Eq.(1), describing the Josephson current, has been the subject of intensive experimental and theoretical studies over several decades, since the discovery of the Josephson effect. The second term, representing the dissipative current, has attracted relatively little attention, both on the theoretical and experimental sides. In the context of SNS junctions with s-wave symmetry of the order parameter in the leads, this problem was considered theoretically in [1][2][3][4][5][6][7], and experimentally in [8]. The common result of these works is that at low temperatures the conductance of the system is proportional to the inelastic relaxation time in the normal metal. A theory of conductance of a junction in the case when the superconducting order parameter has d-wave symmetry has not been developed. In this paper we show that at low temperatures T the conductance, G DN D , is proportional to the square root of the energy relaxation time in the bulk of superconductor, τ in , and that it is much larger than the conductance G N of the normal piece of the junction.The origin of the leading low-temperature contribution to G DN D is similar to the Debye relaxation mechanism in dielectrics, or the Mandelstam-Leontovich mechanism for sound absorption in liquids with internal degrees of freedom [9]. Due to the proximity effect the single particle density of states in the normal region, ν N (ε, φ), becomes ε and φ-dependent. Here ε is the energy of quasiparticle. According to Eq. (2), ν N (ε, φ(t)) changes in time. In the adiabatic approximation the electron population follows the motion of the levels. As a result, the quasiparticle distribution function becomes nonequilibrium. Its relaxation leads to the entropy production, and therefore contributes to the conductance:The equation for the entropy production readṡwhere f (ε, r, t) is the quasiparticle distribution function, f th (ε, r, t) = tanh ε/2T is the equilibrium distribution function, τ in is the inelastic relaxation time, D ij (ε) is the diffusion coefficient, and ν is the reduced density of states, measured in the units of the normal state density of states, ν 0 . We assume that the latter is the same in both metals.The kinetic equation describing the dynamics of quasiparticles has the following form: ν ∂f ∂...

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Nonequilibrium ac Josephson Effect in Mesoscopic Nb-InAs-Nb Junctions

Cited by 40 publications

References 13 publications

Subgap structure in the conductance of a three-terminal Josephson junction

Subgap structure in the conductance of a three-terminal Josephson junction

Subharmonic Shapiro Steps and Assisted Tunneling in Superconducting Point Contacts

Conductance ofd-Wave Superconductor/Normal Metal/d-Wave Superconductor Junctions

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