Nb/InAs nanowire proximity junctions from Josephson to quantum dot regimes

Gharavi, Kaveh; Holloway, Gregory W.; LaPierre, Ray; Baugh, Jonathan

doi:10.1088/1361-6528/aa5643

Cited by 22 publications

(19 citation statements)

References 63 publications

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“…In Fig. 3(b), a second ABS QD 2 is added to the quantum dot separated by 0.35 meV from QD 1 [28]. At low bias, in the blue region, this yields a pair of resonances most clearly seen in the s 0 region.…”

mentioning

confidence: 96%

Mirage Andreev Spectra Generated by Mesoscopic Leads in Nanowire Quantum Dots

Zarassi

Hsu

et al. 2018

Phys. Rev. Lett.

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We study transport mediated by Andreev bound states formed in InSb nanowire quantum dots. Two kinds of superconducting source and drain contacts are used: epitaxial Al/InSb devices exhibit a doubling of tunneling resonances, while in NbTiN/InSb devices Andreev spectra of the dot appear to be replicated multiple times at increasing source-drain bias voltages. In both devices, a mirage of a crowded spectrum is created. To describe the observations a model is developed that combines the effects of a soft induced gap and of additional Andreev bound states both in the quantum dot and in the finite regions of the nanowire adjacent to the quantum dot. Understanding of Andreev spectroscopy is important for the correct interpretation of Majorana experiments done on the same structures.The superconductor-semiconductor hybrid structures are of recent interest due to the possibility of inducing topological superconductivity accompanied by Majorana bound states (MBS) [1][2][3][4]. More generally, when a semiconductor is of finite size, proximity to a superconductor gives rise to subgap quasiparticle excitations, the so-called Andreev bound states (ABS), that appear due to successive Andreev reflections at the interfaces. Single ABS have been demonstrated in a variety of structures including self-assembled quantum dots, semiconductor nanowires, atomic break junctions, carbon nanotubes and graphene [5][6][7][8][9][10][11]. ABS exhibit many similarities to MBS, and therefore ABS can be served as a prototypical system for Majorana studies [12,13]. A powerful experimental method for investigating both MBS and ABS is via tunneling, either from a nanofabricated probe or by scanning tunneling spectroscopy. The latter is typically performed on Yu-Shiba-Rusinov states which are closely analogous to ABS but originate from magnetic impurities in superconductors [14,15].In this paper, we focus on the mesoscopic effects within the tunneling probes. We show that the non-trivial densities of states (DOS) in the probes can drastically affect tunneling characteristics by generating multiple replicas of ABS. To experimentally investigate these effects, we use semiconductor nanowires coupled to superconductors. ABS are induced in a quantum dot by strongly coupling the dot to one superconducting contact. A second superconducting contact and a nanowire segment ad-jacent to it act as a tunneling probe. To explain our observations, we consider the effects of soft induced superconducting gap in the nanowire, and of additional ABS induced in nanowire segments adjacent to the dot. The surprising observation of sub-gap negative differential conductance (NDC) is found to be consistent with a peak in the density of states of the probe at zero chemical potential, which is present even at zero magnetic field. The exact origin of this anomalous density of states remains an open question. Our findings emphasize the importance of understanding the spectral structure of the measuring contacts to interpret tunneling experiments in mesoscopic systems. We expect t...

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confidence: 96%

Mirage Andreev Spectra Generated by Mesoscopic Leads in Nanowire Quantum Dots

Zarassi

Hsu

et al. 2018

Phys. Rev. Lett.

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“…20,21 Recent works reported Josephson effects at high magnetic fields, sufficient to generate unpaired Majorana bound states. 19,[22][23][24] In this Letter we study the critical current as a function of the magnetic field and gate voltage in nanowire Josephson junctions tuned to the mesoscopic few-mode regime. The junctions consist of InSb weak links and NbTiN superconductor contacts.…”

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confidence: 99%

Supercurrent Interference in Few-Mode Nanowire Josephson Junctions

et al. 2017

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Junctions created by coupling two superconductors via a semiconductor nanowire in the presence of high magnetic fields are the basis for the potential detection, fusion, and braiding of Majorana bound states. We study NbTiN=InSb nanowire=NbTiN Josephson junctions and find that the dependence of the critical current on the magnetic field exhibits gate-tunable nodes. This is in contrast with a well-known Fraunhofer effect, under which critical current nodes form a regular pattern with a period fixed by the junction area. Based on a realistic numerical model we conclude that the Zeeman effect induced by the magnetic field and the spin-orbit interaction in the nanowire are insufficient to explain the observed evolution of the Josephson effect. We find the interference between the few occupied one-dimensional modes in the nanowire to be the dominant mechanism responsible for the critical current behavior. We also report a strong suppression of critical currents at finite magnetic fields that should be taken into account when designing circuits based on Majorana bound states.

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“…In the superconducting regime, charge localization gives rise to a strong nonmonotonic behavior of the Josephson current as a function of B due to a Zeeman-induced 0 -p phase transition. Our findings are relevant to experiments aiming at detecting Majorana modes in Josephson junction geometries based on depleted NWs under strong Zeeman fields (28)(29)(30). The anomalous B-field dependence of the critical current, owing to the presence of Majoranas in the 0.52 0.44 0.36 junction (31)(32)(33), may be masked by the localization effects and the Kondo physics discussed here.…”

Section: Discussionmentioning

confidence: 57%

Charge localization and reentrant superconductivity in a quasi-ballistic InAs nanowire coupled to superconductors

et al. 2019

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A semiconductor nanowire with strong spin-orbit coupling in proximity to a superconductor is predicted to display Majorana edge states emerging under a properly oriented magnetic field. The experimental investigation of these exotic states requires assessing the one-dimensional (1D) character of the nanowire and understanding the superconducting proximity effect in the presence of a magnetic field. Here, we explore the quasi-ballistic 1D transport regime of an InAs nanowire with Ta contacts. Fine-tuned by means of local gates, the observed plateaus of approximately quantized conductance hide the presence of a localized electron, giving rise to a lurking Coulomb blockade effect and Kondo physics. When Ta becomes superconducting, this local charge causes an unusual, reentrant magnetic field dependence of the supercurrent, which we ascribe to a 0 - π transition. Our results underline the relevant role of unintentional charge localization in the few-channel regime where helical subbands and Majorana quasi-particles are expected to arise.

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Nb/InAs nanowire proximity junctions from Josephson to quantum dot regimes

Cited by 22 publications

References 63 publications

Mirage Andreev Spectra Generated by Mesoscopic Leads in Nanowire Quantum Dots

Mirage Andreev Spectra Generated by Mesoscopic Leads in Nanowire Quantum Dots

Supercurrent Interference in Few-Mode Nanowire Josephson Junctions

Charge localization and reentrant superconductivity in a quasi-ballistic InAs nanowire coupled to superconductors

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