Mirage Andreev spectra generated by mesoscopic leads in nanowire quantum dots

TL;DR

This paper investigates how mesoscopic leads influence Andreev spectra in InSb nanowire quantum dots, revealing spectral mirages and developing a model to interpret these complex transport phenomena.

Contribution

It introduces a model that explains the replicated and doubled Andreev spectra caused by mesoscopic leads in nanowire quantum dots, advancing understanding of Andreev spectroscopy.

Findings

Doubling of tunneling resonances in epitaxial Al/InSb devices

Replication of Andreev spectra at higher bias in NbTiN/InSb devices

Spectral mirages caused by mesoscopic lead effects

Abstract

We study transport mediated by Andreev bound states formed in InSb nanowire quantum dots. Two kinds of superconducting source and drain contacts are used: epitaxial Al/InSb devices exhibit a doubling of tunneling resonances, while in NbTiN/InSb devices Andreev spectra of the dot appear to be replicated multiple times at increasing source-drain bias voltages. In both devices, a mirage of a crowded spectrum is created. To describe the observations a model is developed that combines the effects of a soft induced gap and of additional Andreev bound states both in the quantum dot and in the finite regions of the nanowire adjacent to the quantum dot. Understanding of Andreev spectroscopy is important for the correct interpretation of Majorana experiments done on the same structures.