Proximity-induced gap in nanowires with a thin superconducting shell

Kiendl, Thomas; Oppen, Felix von; Brouwer, Piet W.

doi:10.1103/physrevb.100.035426

Cited by 29 publications

(21 citation statements)

References 42 publications

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“…This is justified by the small effective transparency of the interface for quasiparticles traveling from the superconductor into the semiconductor: quasiparticles in the superconductor have a much larger Fermi momentum than in the semiconductor. Only quasiparticles moving with a small momentum parallel to the interface can tunnel from the superconductor to the semiconductor, but strong disorder in the superconductor randomizes the momentum direction, resulting in a low-probability of tunneling [46]. Note that electrons from the semiconductor have a high probability of tunneling into the superconductor and reflecting back as a hole, providing Andreev scattering.…”

Section: A Usadel Equationmentioning

confidence: 99%

Topological superconductivity in nanowires proximate to a diffusive superconductor–magnetic-insulator bilayer

et al. 2021

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We study semiconductor nanowires coupled to a bilayer of a disordered superconductor and a magnetic insulator, motivated by recent experiments reporting possible Majorana-zero-mode signatures in related architectures. Specifically, we pursue a quasiclassical Usadel equation approach that treats superconductivity in the bilayer self-consistently in the presence of spin-orbit scattering, magnetic-impurity scattering, and Zeeman splitting induced by both the magnetic insulator and a supplemental applied field. Within this framework we explore prospects for engineering topological superconductivity in a nanowire proximate to the bilayer. We find that a magnetic-insulator-induced Zeeman splitting, mediated through the superconductor alone, cannot induce a topological phase since the destruction of superconductivity (i.e., Clogston limit) preempts the required regime in which the nanowire's Zeeman energy exceeds the induced pairing strength. However, this Zeeman splitting does reduce the critical applied field needed to access the topological phase transition, with fields antiparallel to the magnetization of the magnetic insulator having an optimal effect. Finally, we show that magnetic-impurity scattering degrades the topological phase, and spin-orbit scattering, if present in the superconductor, pushes the Clogston limit to higher fields yet simultaneously increases the critical applied field strength.

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Section: A Usadel Equationmentioning

confidence: 99%

Topological superconductivity in nanowires proximate to a diffusive superconductor–magnetic-insulator bilayer

et al. 2021

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“…On the other hand, if the proximity effect is strong, the bulk superconductor 'metallizes' the semiconducting nanostructure, bringing its parameters closer to the metal values with strongly reduced SOI and g-factors. [214][215][216][217][218] Moreover, due to screening, it is challenging to control the position of the chemical potential in order to tune it to the 'sweet spot'. Thus, future experiments need to find ways to avoid or reduce such metallization effects on the semiconductors.…”

Section: Discussionmentioning

confidence: 99%

Majorana bound states in semiconducting nanostructures

Laubscher,

Klinovaja

2021

Preprint

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In this Tutorial, we give a pedagogical introduction to Majorana bound states (MBSs) arising in semiconducting nanostructures. We start by briefly reviewing the well-known Kitaev chain toy model in order to introduce some of the basic properties of MBSs before proceeding to describe more experimentally relevant platforms. Here, our focus lies on simple 'minimal' models where the Majorana wave functions can be obtained explicitly by standard methods. In a first part, we review the paradigmatic model of a Rashba nanowire with strong spin-orbit interaction (SOI) placed in a magnetic field and proximitized by a conventional s-wave superconductor. We identify the topological phase transition separating the trivial phase from the topological phase and demonstrate how the explicit Majorana wave functions can be obtained in the limit of strong SOI. In a second part, we discuss MBSs engineered from proximitized edge states of two-dimensional (2D) topological insulators. We introduce the Jackiw-Rebbi mechanism leading to the emergence of bound states at mass domain walls and show how this mechanism can be exploited to construct MBSs. Due to their recent interest, we also include a discussion of Majorana corner states in 2D second-order topological superconductors. This Tutorial is mainly aimed at graduate students-both theorists and experimentalists-seeking to familiarize themselves with some of the basic concepts in the field.

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“…and is constructed out of the tunneling matrix elements t 1 = t 2 in N 1 and N 2 and the tunneling matrix element t S in S. We define the Heaviside function Θ(n) with Θ(0) = 1/2 throughout. The difference between the tunneling matrix elements of the superconducting and the normal sections arises due to the mass renormalization inside the superconducting section caused by metallization effects induced by the thin superconducting shell [72][73][74][75][76][77]. The chemical potential has a similar structure…”

Section: A Non-topological Nanowirementioning

confidence: 99%

Local and non-local quantum transport due to Andreev bound states in finite Rashba nanowires with superconducting and normal sections

Hess,

Legg,

Loss

et al. 2021

Preprint

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We analyze Andreev bound states (ABSs) that form in normal sections of a Rashba nanowire that is only partially covered by a superconducting layer. These ABSs are localized close to the ends of the superconducting section and can be pinned to zero energy over a wide range of magnetic field strengths even if the nanowire is in the non-topological regime. For finite-size nanowires (typically 1 µm in current experiments), the ABS localization length is comparable to the length of the nanowire. The probability density of an ABS is therefore non-zero throughout the nanowire and differential-conductance calculations reveal a correlated zero-bias peak (ZBP) at both ends of the nanowire. When a second normal section hosts an additional ABS at the opposite end of the superconducting section, the combination of the two ABSs can mimic the closing and reopening of the bulk gap in local and non-local conductances accompanied by the appearance of the ZBP. These signatures are reminiscent of those expected for Majorana bound states (MBSs) but occur here in the non-topological regime. Our results demonstrate that conductance measurements of correlated ZBPs at the ends of a typical superconducting nanowire or an apparent closing and reopening of the bulk gap in the local and non-local conductance are not conclusive indicators for the presence of MBSs.

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Proximity-induced gap in nanowires with a thin superconducting shell

Cited by 29 publications

References 42 publications

Topological superconductivity in nanowires proximate to a diffusive superconductor–magnetic-insulator bilayer

Topological superconductivity in nanowires proximate to a diffusive superconductor–magnetic-insulator bilayer

Majorana bound states in semiconducting nanostructures

Local and non-local quantum transport due to Andreev bound states in finite Rashba nanowires with superconducting and normal sections

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