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

TL;DR

This paper investigates superconducting proximity effects in Nb/InAs nanowire Josephson junctions, revealing two quantum transport regimes and discussing their implications for Majorana fermion research.

Contribution

It experimentally characterizes contact transparency, phase coherence, and transport regimes in Nb/InAs nanowire junctions, including modeling Andreev Bound States in quantum dot regime.

Findings

High contact transparency (~0.7) achieved.

Observation of dissipationless current up to 100 nA.

Detection of Andreev Bound States and their modeling.

Abstract

The superconducting proximity effect is probed experimentally in Josephson junctions fabricated with InAs nanowires contacted by Nb leads. Contact transparencies $t \sim 0.7$ are observed. The electronic phase coherence length at low temperatures exceeds the channel length. However, the elastic scattering length is a few times shorter than the channel length. Electrical measurements reveal two regimes of quantum transport: (i) the Josephson regime, characterized by a dissipationless current up to $\sim 100$ nA, and (ii) the quantum dot regime, characterized by the formation of Andreev Bound States (ABS) associated with spontaneous quantum dots inside the nanowire channel. In regime (i), the behaviour of the critical current $I_c$ versus an axial magnetic field $B_{||}$ shows an unexpected modulation and persistence to fields $>2$ T. In the quantum dot regime, the ABS are modelled as the current-biased solutions of an Anderson-type model. The applicability of devices in both transport regimes to Majorana fermion experiments is discussed.