Mechanisms of Andreev reflection in quantum Hall graphene

Manesco, Antonio L. R.; Flór, Ian Matthias; Liu, Chunxiao; Akhmerov, A. R.

doi:10.21468/scipostphyscore.5.3.045

Cited by 17 publications

(3 citation statements)

References 34 publications

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“…Robust Andreev reflection, being enabled by disorder, is naturally sensitive to its realization in a sample. As a result, the charge transport varies stochastically with control parameters such as the magnetic field or the electron density, as is observed both in experiment 8 and in numerical simulation 11 .…”

Section: Introductionmentioning

confidence: 71%

Disorder-enabled Andreev reflection of a quantum Hall edge

2023

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We develop a theory of charge transport along the quantum Hall edge proximitized by a superconductor. We note that generically Andreev reflection of an edge state is suppressed if translation invariance along the edge is preserved. Disorder in a “dirty” superconductor enables the Andreev reflection but makes it random. As a result, the conductance of a proximitized segment is a stochastic quantity with giant sign-alternating fluctuations and zero average. We find the statistical distribution of the conductance and its dependence on electron density, magnetic field, and temperature. Our theory provides an explanation of a recent experiment with a proximitized edge state.

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Section: Introductionmentioning

confidence: 71%

Disorder-enabled Andreev reflection of a quantum Hall edge

2023

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“…Firstly, some experiments observe a systematically negative nonlocal conductance [2,3], whereas other works see mesoscopic conductance fluctuations with zero average [4]. The latter is a natural result of an interplay between multiple Andreev reflections and disorder, and is therefore expected [5,6]. To the best of my knowledge, the former lacks microscopic theory so far, and remains a puzzle.…”

mentioning

confidence: 99%

Persistently negative: nonlocal Andreev reflection in a chiral mode

Akhmerov

2023

Journal Club for Condensed Matter Physics

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The quest for combining superconductivity and the quantum Hall effect is several decades old. The conceptual idea is simple and powerful: a chiral edge mode is a one-way street. Therefore, when an electron reflects from an edge state into a superconductor, the resulting particle-no matter whether electron or hole-propagates in the same direction as the incoming electron. This way, the spatial separation between electrons and holes is maximal and the local reflection is fully prohibited. If the probability for the hole to exit the superconductor is larger, a positive voltage between the injecting electrode and the superconductor results in a negative current between the superconductor and the collecting electrode, providing a straightforward signature of nonlocal Andreev reflection.A related phenomenon, quantum Hall supercurrent, appears when two superconducting electrodes are connected by a quantum Hall edge. Its hallmark is the periodicity of the supercurrent with the number of normal (h/e) and not superconducting (h/2e) flux quanta of magnetic field through the junction area. The change in periodicity compared to the regular Fraunhofer pattern in Josephson junctions also arises due to the chiral nature of the edge mode: all quasiparticles carrying supercurrent must encircle the complete sample. Just like Andreev reflection, quantum Hall supercurrent is a nonlocal phenomenon that requires coherent transport of quasiparticles in contact with a superconducting electrode. Both are therefore suppressed by superconducting vortices that act like quasiparticle sinks and by dephasing due to inelastic scattering.

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“…The early search for Andreev reflection in QH–SC systems focused on InAs and InGaAs semiconductor magneto-resistance oscillations at relatively low magnetic fields followed later by reports of induced superconductivity in QH states . More recently there have been reports of observation of induced superconductivity, , cross Andreev reflection, , edge state mediated supercurrent, and interference of chiral Andreev edge states − in graphene. To make further progress, it is essential to reliably demonstrate the ability to induce robust superconducting correlations into the edge modes of a QH state.…”

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confidence: 99%

Induced Superconducting Pairing in Integer Quantum Hall Edge States

Hatefipour¹,

Cuozzo²,

Kanter³

et al. 2022

Nano Lett.

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Indium arsenide (InAs) near surface quantum wells (QWs) are promising for the fabrication of semiconductor–superconductor heterostructures given that they allow for a strong hybridization between the two-dimensional states in the quantum well and the ones in the superconductor. In this work, we present results for InAs QWs in the quantum Hall regime placed in proximity of superconducting NbTiN. We observe a negative downstream resistance with a corresponding reduction of Hall (upstream) resistance, consistent with a very high Andreev conversion. We analyze the experimental data using the Landauer-Büttiker formalism, generalized to allow for Andreev reflection processes. We attribute the high efficiency of Andreev conversion in our devices to the large transparency of the InAs/NbTiN interface and the consequent strong hybridization of the QH edge modes with the states in the superconductor.

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Mechanisms of Andreev reflection in quantum Hall graphene

Cited by 17 publications

References 34 publications

Disorder-enabled Andreev reflection of a quantum Hall edge

Disorder-enabled Andreev reflection of a quantum Hall edge

Persistently negative: nonlocal Andreev reflection in a chiral mode

Induced Superconducting Pairing in Integer Quantum Hall Edge States

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