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

Abstract

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.

Zeeman-driven parity transitions in an Andreev quantum dot

“…Magnetic-field driven parity transitions in S-QD-S junctions have previously been observed as zeros of a arXiv:2101.09706v1 [cond-mat.mes-hall] 24 Jan 2021 Ti/Au Al InAs reentrant critical current [36] or via direct spectroscopy of the QD [31,35]. Related measurements in N-QD-S devices showed gate voltage and field-driven parity transition as ZBCs [27,32].…”

Multiple Andreev reflections and Shapiro steps in a Ge-Si nanowire Josephson junction

“…Josephson junctions are defined as a weak link between two superconducting reservoirs, which allows a supercurrent to be transported through intrinsically non-superconducting materials, as long as the junction is shorter than the coherence length [1,2]. While early Josephson junctions realized a weak link by using thin layers of oxide, micro-constrictions, point contacts or grain boundaries [3][4][5][6][7], access to complex mesoscopic semiconducting materials have led to Josephson junctions in which control over the charge carrier density enables in situ tuning of the junction transparency and critical current [8][9][10][11][12][13].…”

Supercurrent Detection of Topologically Trivial Zero-Energy States in Nanowire Junctions

“…These zeroenergy levels, appearing in the QD regime, are however somewhat sensitive to SOC [44], with very large SOC inducing level repulsion, which gaps the spectrum and thus destroys the supercurrent π-shift, see SM [55]. Interestingly, QD levels in clearly non-topological Josephson junctions have previously been shown to change the state of the junction from 0 to π with increasing magnetic field and also associated with a spin exchange [19,67,[69][70][71][72][73][74][75], fully consistent with our findings.…”