Coherent diffusive transport mediated by Andreev reflections at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>V</mml:mi><mml:mo>=</mml:mo><mml:mi>Δ</mml:mi><mml:mo>/</mml:mo><mml:mi>e</mml:mi></mml:math>in a mesoscopic superconductor/semiconductor/superconductor junction

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

Section: Prb 62 5355 Brief Reportssupporting

confidence: 70%

Section: Prb 62 5355 Brief Reportsmentioning

confidence: 99%

mentioning

confidence: 99%

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Mesoscopic proximity effect probed through superconducting tunneling contacts

Wilhelm

Golubov

2000

“…While most experimental and theoretical investigations of MAR have concerned two-terminal structures, multiterminal geometries with all superconducting leads have also been studied. Phase dependent MAR-transport in SNS-interferometers was investigated experimentally in a diffusive conductor [11] and theoretically in a single mode junction [12]. In an incoherent three-terminal junction, the current cross-correlation between S leads was predicted to be strongly enhanced due to MARs [13].…”

mentioning

confidence: 99%

Multiple Andreev reflections in hybrid multiterminal junctions

Houzet

Samuelsson

2010

We investigate theoretically charge transport in hybrid multiterminal junctions with superconducting leads kept at different voltages. It is found that multiple Andreev reflections involving several superconducting leads give rise to rich subharmonic gap structures in the current-voltage characteristics. The structures are evidenced numerically in junctions in the incoherent regime.Comment: 5 pages, 3 figure

“…This subharmonic gap structure is explained by multiple Andreev reflection ͑MAR͒ and has been investigated in detail in various mesoscopic systems including superconductor-normal-metal-superconductor ͑SNS͒ plane junctions, superconductor-insulator-superconductor ͑SIS͒ junctions, and quantum point contacts both theoretically [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and experimentally. [15][16][17][18][19][20] The differential conductance dJ / dV of SNS, SIS, and nonmagnetic quantum point contacts exhibits a number of peaks at eV=2⌬ / n in the limiting regimes of short ballistic and diffusive and long ͑in comparison with the superconducting coherence length ͒ diffusive weak links. In the intermediate regime ϳ d, when the interplay between proximity effect and MARs takes place, the conductance subgap structure of SNS voltagebiased diffusive junction modifies and has an additional maximum at roughly eVϳ ⌬ + ⌬ g .…”

Section: Introductionmentioning

confidence: 99%

Influence of spin filtering and spin mixing on the subgap structure ofI−Vcharacteristics in a superconducting quantum point contact

Bobkova

Bobkov

2007

The effect of spin filtering and spin mixing on the dc electric current for voltage biased magnetic quantum point contact with superconducting leads is theoretically studied. The I-V characteristics are calculated for the whole range of spin filtering and spin mixing parameters. It is found that with increasing of spin filtering, the subharmonic step structure of the dc electric current, typical for low-transparency junction and junction without considerable spin filtering, qualitatively changes. In the lower voltage region and for small enough spin mixing the peak structure arises. When spin mixing increases the peak subgap structure evolves to the step structure. The voltages where subharmonic gap features are located are found to be sensitive to the value of spin filtering. The positions of peaks and steps are calculated analytically and the evolution of the subgap structure from well-known tunnel limit to the large spin filtering case is explained in terms of multiple Andreev reflection ͑MAR͒ processes. In particular, it is found that for large spin filtering the subgap feature at eV k arises from 2kth and ͑2k ±1͒th order MAR processes, while in the tunnel limit the step at eV n is known to result from nth order MAR process.