Proximity effects and Andreev reflection in a mesoscopic SNS junction with perfect NS interfaces (original) (raw)
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Mesoscopic proximity effect in double-barrier superconductor/normal-metal junctions
Physical Review B, 2002
We report transport measurements down to T = 60mK of SININ and SNIN structures in the diffusive limit. We fabricated Al − AlOx/Cu/AlOx/Cu (SININ) and Al/Cu/AlOx/Cu (SNIN) vertical junctions. For the first time, a zero bias anomaly was observed in a metallic SININ structure. We attribute this peak of conductance to coherent multi-reflections of electrons between the two tunnel barriers. This conductance maximum is quantitatively fitted by the relevant theory of mesoscopic SININ structures. When the barrier at the SN interface is removed (SNIN structure), we observe a peak of conductance at finite voltage accompagnied by an excess of sub-gap conductance.
Solid State Communications, 1988
Andreev reflections are a phenomenon typical for inhomogeneous, BCS-like superconductors which have Cooper pairs in the ground state and can be described by the Bogoliubov-de Gennes equations. In voltage biased superconductor (S) --normal metal (N) --super conductor (S) junctions Andreev reflections are predicted to cause negative differential conductivity for sufficiently large mean free paths in the N-region and temperatures not too close to T~. Observation of this effect in SNS-junctions with high-T~ superconductors would indicate the presence of Cooper pairs.
Jetp Letters, 2005
We have investigated low-temperature transport properties of two-dimensional arrays of superconductor-normal-metal-superconductor (SNS) junctions. It has been found that in twodimensional arrays of SNS junctions (i) a change in the energy spectrum within an interval of the order of the Thouless energy is observed even when the thermal broadening far exceeds the Thouless energy for a single SNS junction; (ii) the manifestation of the subharmonic energy gap structure (SGS) with high harmonic numbers is possible even if the energy relaxation length is smaller than that required for the realization of a multiple Andreev reflection in a single SNS junction. These results point to the synchronization of a great number of SNS junctions. A mechanism of the SGS origin in two-dimensional arrays of SNS junctions, involving the processes of conventional and crossed Andreev reflection, is proposed.
Measurement of junction conductance and proximity effect at superconductor/semiconductor junctions
Eprint Arxiv 1402 6055, 2014
The superconducting proximity effect has played an important role in recent work searching for Majorana modes in thin semiconductor devices. Using transport measurements to quantify the changes in the semiconductor caused by the proximity effect provides a measure of dynamical processes such as screening and scattering. However, in a two terminal measurement the resistance due to the interface conductance is in series with resistance of transport in the semiconductor. Both of these change, and it is impossible to separate them without more information. We have devised a new three terminal device that provides two resistance measurements that are sufficient to extract both the junction conductance and the two dimensional sheet resistance under the superconducting contact. We have compared junctions between Nb and InAs and Nb and 30% InGaAs all grown before being removed from the ultra high vacuum molecular beam epitaxy growth system. The most transparent junctions are to InAs, where the transmission coefficient per Landauer mode is greater than 0.6. Contacts made with ex-situ deposition are substantially more opaque. We find that for the most transparent junctions, the largest fractional change as the temperature is lowered is to the resistance of the semiconductor.
Resistance of superconductor-normal-metal-superconductor (SNS) junctions
Journal of Experimental and Theoretical Physics Letters, 1997
It is shown that the conductance of a superconductor-normal metal-superconductor junction can exhibit a significant dependence on the phase of the superconducting order parameter in the situation when the size of the normal region of the junction is much larger than the normal metal coherence length and the critical current of the junction is already exponentially small. The period of the conductance oscillations as a function of the phase can be equal to π or 2π depending on parameters of the system. Suggested PACS index category: 05.20-y, 82.20-w
Andreev reflection and excess noise in diffusive SNS junctions
Physica C: Superconductivity, 2001
We investigated superconductor/normal metal/superconductor (SNS) junctions made of short Au or Cu wires between Nb or Al banks. The Nb based junctions display inherent electron heating eects induced by the high thermal resistance of the NS boundaries. The Al based junctions show in addition subharmonic gap structures in the dierential conductance dI/dV and a pronounced peak in the excess noise at very low voltages V. We suggest that the noise peak is caused by¯uctuations of the supercurrent at the onset of Josephson coupling between the superconducting banks. At intermediate temperatures where the supercurrent is suppressed a noise contribution G 1=V remains, which re¯ects the strong nonequilibrium of quasiparticles even at very small voltages.
Physica B-condensed Matter, 1998
Particularly high transmittivity superconductor-semiconductor barriers formed by MBE growth have been used to form short Josephson planar type Superconductor-Normal-metal-Superconductor (SNS) Josephson junctions with lengths down to 1 m. In these junctions the quasiparticles move diffusively across the normal region and carry along the phase information given to them by Andreev reflections at both SN boundaries. In order to probe the importance of the coherent transport of quasiparticles in the normal region, we formed one of the superconducting electrodes of the junction as an open loop i.e. an SNS S junction. The total transmission probability through this junction which is modulated by the external magnetic flux through the loop, depends on the coherence of the trajectories going across from S to S and from S to S . Oscillations of the conductance in this type of sample versus magnetic field was observed both at » "! "0 and » "! " /e"163 V. At intermediate as well as higher voltages no oscillations were observed. 1998 Elsevier Science B.V. All rights reserved.