Andreev reflection and enhanced subgap conductance in NbN∕Au∕InGaAs-InP junctions

Batov, I. E.; Schaepers, Th.; Golubov, A. A.; Ustinov, A. V.

doi:10.1063/1.1783612

Cited by 18 publications

(16 citation statements)

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“…The choice of the NbN/Au system was motivated by our previous studies, where an Au interlayer helped achieving a high S/2DEG interface transparency while maintaining a high critical field of the superconductor. 29 Complementary to the work of Eroms et al, 28 we observe a suppression of enhanced oscillations in the magnetoresistance when a dc bias current across the junction exceeds a critical value or the temperature is increased above a critical temperature. 29 We compare our measurements of the NbN/Au/2DEG structures to that of similar structures with normal metal electrodes connected to the 2DEG.…”

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“…29 Complementary to the work of Eroms et al, 28 we observe a suppression of enhanced oscillations in the magnetoresistance when a dc bias current across the junction exceeds a critical value or the temperature is increased above a critical temperature. 29 We compare our measurements of the NbN/Au/2DEG structures to that of similar structures with normal metal electrodes connected to the 2DEG. Our interpretation of the experimental findings is based on recent theoretical models describing Andreev reflection across a S/2DEG interface in the presence of a magnetic field.…”

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Andreev reflection and strongly enhanced magnetoresistance oscillations inGaxIn1−xAs∕InP<

et al. 2007

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We study the magnetotransport in small hybrid junctions formed by high-mobility GaxIn1−xAs/InP heterostructures coupled to superconducting (S) and normal metal (N) terminals. Highly transmissive superconducting contacts to a two-dimensional electron gas (2DEG) located in a GaxIn1−xAs/InP heterostructure are realized by using a Au/NbN layer system. The magnetoresistance of the S/2DEG/N structures is studied as a function of dc bias current and temperature. At bias currents below a critical value, the resistance of the S/2DEG/N structures develops a strong oscillatory dependence on the magnetic field, with an amplitude of the oscillations considerably larger than that of the reference N/2DEG/N structures. The experimental results are qualitatively explained by taking Andreev reflection in high magnetic fields into account.

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confidence: 83%

Andreev reflection and strongly enhanced magnetoresistance oscillations inGaxIn1−xAs∕InP<

et al. 2007

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“…In addition, the high carrier mobility attainable in semiconductors in combination with the phase-coherent Andreev reflection leads to novel unique phenomena in the magnetotransport. [5][6][7] Usually for these devices the semiconductor is patterned by conventional lithography. As an elegant alternative one can also directly create semiconductor nanostructures, i.e.…”

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Josephson supercurrent in Nb/InN-nanowire/Nb junctions

Frielinghaus

Batov

Weides

et al. 2010

Applied Physics Letters

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We experimentally studied the Josephson supercurrent in Nb/InN-nanowire/Nb junctions. Large critical currents up to 5.7 µA have been achieved, which proves the good coupling of the nanowire to the superconductor. The effect of a magnetic field perpendicular to the plane of the Josephson junction on the critical current has been studied. The observed monotonous decrease of the critical current with magnetic field is explained by the magnetic pair-breaking effect in planar Josephson junctions of ultra-narrow width [J. C. Cuevas and F. S. Bergeret, Phys. Rev. Lett. 99, 217002 (2007)] Superconductor/normal-conductor/superconductor (SNS) junctions with a semiconductor employed as the N-weak link material offer the great advantage that here the Josephson supercurrent can be controlled by means of the field effect. 1,2 Gate-controlled superconductor/semiconductor hybrid devices such as superconducting field effect transistors 3 or split-gate structures 4 have been fabricated which find no counterpart in conventional SNS structures. In addition, the high carrier mobility attainable in semiconductors in combination with the phase-coherent Andreev reflection leads to novel unique phenomena in the magnetotransport. 5-7 Usually for these devices the semiconductor is patterned by conventional lithography. As an elegant alternative one can also directly create semiconductor nanostructures, i.e. nanowires, by epitaxial growth. 8 By using InAs nanowires connected to superconducting electrodes tunable Josephson supercurrents, supercurrent reversal, and Kondo-enhanced Andreev tunneling have been realized. [9][10][11] Among the various materials used for semiconductor nanowires InN is of particular interest for semiconductor/superconductor hybrid structures, since the surface accumulation layer in InN can provide a sufficiently low resistive contact to superconducting electrodes. 12-14 Due to almost ideal crystalline properties of InN nanowires electronic transport along the wires, contacted by normal metal electrodes, shows quantization phenomena, i.e. flux periodic magnetoconductance oscillations. 15 Furthermore, the carrier concentration in the surface electron gas is of the order of 10 13 cm −2 and thus about a factor of ten larger than in InAs. Consequently when combined with superconducting electrodes one can expect low resistive SNS junctions.Here, we report on transport studies of Nb/InNnanowire/Nb junctions. We succeeded in observing a pronounced Josephson supercurrent and a relatively large I c R N product of up to 0.44 mV. The latter factor, the critical current times the normal resistance, is an important figure of merit for Josephson junctions. We devoted special attention to the dependence of the critical current I c on an external magnetic field B, where a monotonous decrease of I c with B was found. This experimental finding is interpreted in the framework of a recent theoretical model for the proximity effect in narrow-width junctions with dimensions comparable or smaller than the magnetic length ξ B = Φ 0 /B,...

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“…To enter the regime of a fully developed quantum Hall effect external fields of several Tesla are required. Experiments have been performed with high critical field superconductors, such as NbN [11,12] or sintered SnAu [13], each of which suffer from technological difficulties, making the interpretation of the experiments in the quantum Hall regime difficult. In this work, however, we report clear evidence of the influence of Andreev reflection on transport in edge states using the well established Nb-InAs system.…”

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Andreev Reflection at High Magnetic Fields: Evidence for Electron and Hole Transport in Edge States

et al. 2005

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We have studied magnetotransport in arrays of niobium filled grooves in an InAs/AlGaSb heterostructure. The critical field of up to 2.6 T permits to enter the quantum Hall regime. In the superconducting state, we observe strong magnetoresistance oscillations, whose amplitude exceeds the Shubnikov-de Haas oscillations by a factor of about two, when normalized to the background. Additionally, we find that above a geometry-dependent magnetic field value the sample in the superconducting state has a higher longitudinal resistance than in the normal state. Both observations can be explained with edge channels populated with electrons and Andreev reflected holes.The analysis of superconductor-semiconductor structures has been an active field of research in recent years (see, e.g., Ref. 1 and references therein). The versatility of semiconductors and the high mobilities attainable in heterostructures in combination with the retroreflecting and phase coherent process of Andreev reflection [2] have allowed to observe a number of unique phenomena. By now, experiments in the regime of low magnetic fields, i.e. no larger than a few flux quanta per junction area, are well established. Gateable Josephson currents [3], quasiparticle interference [4], phase coherent oscillations [5] and an induced superconducting gap [6] have been observed, to name a few.In the high-field regime, experimental evidence is much less abundant. A number of theoretical papers have dealt with Andreev reflection at high fields [7,8,9,10]. Notably, Ref. 7 describes how edge channels in the quantum Hall regime are formed of electron and hole states. To enter the regime of a fully developed quantum Hall effect external fields of several Tesla are required. Experiments have been performed with high critical field superconductors, such as NbN [11,12] or sintered SnAu [13], each of which suffer from technological difficulties, making the interpretation of the experiments in the quantum Hall regime difficult. In this work, however, we report clear evidence of the influence of Andreev reflection on transport in edge states using the well established Nb-InAs system. The critical field of up to 2.6 T permits to enter the quantum Hall regime at high filling factors.For the sample geometry we have chosen an array of niobium filled grooves in an InAs-AlGaSb heterostructure containing a high-mobility two-dimensional electron gas (2DEG). A similar arrangement has been studied previously [14,15] in low magnetic fields. An important difference to single S-2DEG-S junctions is that the voltage Right: A scanning electron micrograph of the sample taken at the mesa edge. A cross section of the sample is also shown.

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Andreev reflection and enhanced subgap conductance in NbN∕Au∕InGaAs-InP junctions

Cited by 18 publications

References 50 publications

Andreev reflection and strongly enhanced magnetoresistance oscillations inGaxIn1−xAs∕InP<

Andreev reflection and strongly enhanced magnetoresistance oscillations inGaxIn1−xAs∕InP<

Josephson supercurrent in Nb/InN-nanowire/Nb junctions

Andreev Reflection at High Magnetic Fields: Evidence for Electron and Hole Transport in Edge States

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