Replicas of Andreev spectra in InSb nanowires

A superconducting contact to a quantum dot can induce electron-hole correlations known as Andreev bound states (ABSs) inside the dot. We study transport through ABSs in InSb nanowires with superconducting contacts as both source and drain. Anomalous transport resonances are observed in these systems, namely one or more (up to 4) replicas of Andreev spectra at higher source-drain biases, as well as negative differential conductance shadows of the resonances inside the induced gap. We develop a model that captures these features by considering the effect of a soft-gap superconducting probe, and of additional ABSs induced in the dot, and in the nanowire segments adjacent to the dot. Our findings extend the framework for the interpretation of tunneling experiments in mesoscopic systems, and specifically of Majorana bound states which are studied with semiconductor nanowire probes similar to those used here.