Temperature dependence of critical currents in Nb/InAs/Nb Josephson junction arrays

Correa, Juliet; Eckhause, T. A.; Gwinn, E. G.; Thomas, M.

doi:10.1016/s1386-9477(01)00411-8

Cited by 3 publications

(3 citation statements)

References 6 publications

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“…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.…”

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confidence: 53%

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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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supporting

confidence: 53%

“…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 probes are located in the 2DEG.…”

supporting

confidence: 53%

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

et al. 2005

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“…Because the film on the step is quite thin, a large step height can result in microscopic discontinuities or granularity in the film which lead to a multiplicity or an array of weak link junction acting in a series network. Similar successive jumps in I -V were reported for Nb/InAs/Nb tri-layer proximity 45-junction arrays [49], and have been explained by a simple series network of junctions, each with slightly different normal state resistance. Niobium has a rather short coherence length and thus other physical characteristics at the step edge (e.g., non-uniform barrier thickness, structural defects, electron traps, grainboundary impurities) which suppress the energy gap can lead to non-ideal I -V characteristics.…”

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confidence: 76%

Niobium step-edge superconducting junctions

Savvides¹

2008

Supercond. Sci. Technol.

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Niobium junctions based on a step milled onto SiO2/Si substrates were fabricated by patterning niobium thin films of thickness d = 25–200 nm to form step-edge junctions of height h = 25–200 nm and length L = 1.5–20 µm. Measurements of the current–voltage (I–V) characteristics reveal a strong dependence on the ratio d/h (0.25–5.3), with junctions changing from non-hysteretic to strongly hysteretic in I–V as d/h changes from less than to greater than unity. The temperature dependence of Ic(T = 1.5–7 K) shows a step-like behavior that is indicative of complex vortex motion within the junctions.

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