X-shaped and Y-shaped Andreev resonance profiles in a superconducting quantum dot

Mi, Shuo; Pikulin, Dmitry I.; Marciani, Marco; Beenakker, C. W. J.

doi:10.1134/s1063776114120176

Cited by 32 publications

(42 citation statements)

References 33 publications

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“…1). Our central result expands and substantially generalizes on the generic class D "sticking ZBCP" [35] scenario -i.e., a non-quantized conductance peak that remains at zero bias as a single continuous parameter is tuned (this was also called a "Y-shaped Andreev resonance" in Ref. 35).…”

supporting

confidence: 59%

“…Zeeman field, gate voltages, tunnel barrier) in a systematic way is practically guaranteed to produce these "false positive" apparently quantized, but nevertheless trivial, ZBCPs. Our theoretical starting point is a class D random matrix ensemble [31,[33][34][35]. The model is maximally generic, since we impose no constraint other than particle-hole symmetry on the Hamiltonian, which holds for every experimental Majorana platform.…”

mentioning

confidence: 99%

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Generic quantized zero-bias conductance peaks in superconductor-semiconductor hybrid structures

Pan

Cole

et al. 2020

Phys. Rev. B

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We show theoretically that quantized zero-bias conductance peaks should be ubiquitous in superconductor-semiconductor hybrids by employing a zero-dimensional random matrix model with continuous tuning parameters. We demonstrate that NS junction conductance spectra can be generically obtained in this model replicating all features seen in recent experimental results. The theoretical quantized conductance peaks, which explicitly do not arise from spatially isolated Majorana zero modes, are easily found by preparing a contour plot of conductance over several independent tuning parameters, mimicking the effect of Zeeman splitting and voltages on gates near the junction. This suggests that even stable, apparently quantized, conductance peaks need not correspond to isolated Majorana modes; rather the a priori expectation should be that such quantized peaks generically occupy a significant fraction of the high-dimensional tuning parameter space that characterize the NS tunneling experiments.

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supporting

confidence: 59%

mentioning

confidence: 99%

Generic quantized zero-bias conductance peaks in superconductor-semiconductor hybrid structures

Pan

Cole

et al. 2020

Phys. Rev. B

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“…If the scattering region is additionally strongly coupled to a normal lead, a persistent zero-bias peak in the Andreev conductance is formed [43][44][45]. In our case, we expect such a peak to develop in the presence of a discrete vortex, and to disappear in its absence.…”

Section: Conclusion and Discussionmentioning

confidence: 89%

Single fermion manipulation via superconducting phase differences in multiterminal Josephson junctions

2014

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We show how the superconducting phase difference in a Josephson junction may be used to split the Kramers degeneracy of its energy levels and to remove all the properties associated with time-reversal symmetry. The superconducting phase difference is known to be ineffective in two-terminal short Josephson junctions, where irrespective of the junction structure the induced Kramers degeneracy splitting is suppressed and the ground state fermion parity must stay even, so that a protected zero-energy Andreev level crossing may never appear. Our main result is that these limitations can be completely avoided by using multiterminal Josephson junctions. There the Kramers degeneracy breaking becomes comparable to the superconducting gap, and applying phase differences may cause the change of the ground state fermion parity from even to odd. We prove that the necessary condition for the appearance of a fermion parity switch is the presence of a "discrete vortex" in the junction: the situation when the phases of the superconducting leads wind by 2π . Our approach offers strategies for creation of Majorana bound states as well as spin manipulation. Our proposal can be implemented using any low density, high spin-orbit material such as InAs quantum wells, and can be detected using standard tools.

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“…These states are thus no longer orthogonal to each other, and the spin-orbit mediated overlap between them causes energy splitting, leading to level repulsion [40][41][42]. This level repulsion, which is generic in class D systems in the presence of superconductivity, magnetic field and spin-orbit coupling [43,44], can be extracted from the low energy nanowire spectrum as measured by tunneling spectroscopy [45].…”

Section: Level Repulsion Due To Spin-orbit Couplingmentioning

confidence: 99%

Electric field tunable superconductor-semiconductor coupling in Majorana nanowires

et al. 2018

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We study the effect of external electric fields on superconductor-semiconductor coupling by measuring the electron transport in InSb semiconductor nanowires coupled to an epitaxially grown Al superconductor. We find that the gate voltage induced electric fields can greatly modify the coupling strength, which has consequences for the proximity induced superconducting gap, effective g-factor, and spin-orbit coupling, which all play a key role in understanding Majorana physics. We further show that level repulsion due to spin-orbit coupling in a finite size system can lead to seemingly stable zero bias conductance peaks, which mimic the behavior of Majorana zero modes. Our results improve the understanding of realistic Majorana nanowire systems. gate induced electric fields. Due to the change in coupling, the renormalization of material parameters is altered, as evidenced by a change in the effective g-factor of the hybrid system. Furthermore, the electric field is shown to affect the spin-orbit interaction, revealed by a change in the level repulsion between Andreev states. Our experimental findings are corroborated by numerical simulations. Experimental set-upWe have performed tunneling spectroscopy experiments on four InSb-Al hybrid nanowire devices, labeled A-D, all showing consistent behavior. The nanowire growth procedure is described in [20]. A scanning electron micrograph (SEM) of device A is shown in figure 1(a). Figure 1(b) shows a schematic of this device and the measurement set-up. For clarity, the wrap-around tunnel gate, tunnel gate dielectric and contacts have been removed on one side. A normal-superconductor (NS) junction is formed between the part of the nanowire covered by a thin shell of aluminum (10 nm thick, indicated in green, S), and the Cr /Au contact (yellow, N). The transmission of the junction is controlled by applying a voltage V Tunnel to the tunnel gate (red), galvanically isolated from the nanowire by 35 nm of sputtered SiN x dielectric. The electric field is induced by a global back gate voltage V BG , except in the case of device B, where this role is played by the side gate voltage V SG . Further details on device fabrication and design are included in appendices A and B. To obtain information about the density of states (DOS) in the proximitized nanowire, we measure the differential conductance dI/dV Bias as a function of applied bias voltage V Bias . In the following, we will label this quantity as dI/dV for brevity. A magnetic field is applied along the nanowire direction (x-axis in figures 1(b), (c)). All measurements are performed in a dilution refrigerator with a base temperature of 20 mK. Theoretical modelThe device geometry used in the simulation is shown in figure 1(c). We consider a nanowire oriented along the x-direction, with a hexagonal cross-section in the yz-plane. The hybrid superconductor-nanowire system is described by the Bogoliubov-de Gennes (BdG) Hamiltonian

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X-shaped and Y-shaped Andreev resonance profiles in a superconducting quantum dot

Cited by 32 publications

References 33 publications

Generic quantized zero-bias conductance peaks in superconductor-semiconductor hybrid structures

Generic quantized zero-bias conductance peaks in superconductor-semiconductor hybrid structures

Single fermion manipulation via superconducting phase differences in multiterminal Josephson junctions

Electric field tunable superconductor-semiconductor coupling in Majorana nanowires

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