Probing proximity induced superconductivity in InAs nanowire using built-in barriers

Abstract

Bound states in superconductor-nanowire hybrid devices play a central role, carrying information on the ground states properties (Shiba or Andreev states) or on the topological properties of the system (Majorana states). The spectroscopy of such bound states relies on the formation of welldefined tunnel barriers, usually defined by gate electrodes, which results in smooth tunnel barriers.Here we used thin InP segments embedded into InAs nanowire during the growth process to form a sharp built-in tunnel barrier. Gate dependence and thermal activation measurements have been used to confirm the presence and estimate the height of this barrier. By coupling these wires to superconducting electrodes we have investigated the gate voltage dependence of the induced gap in the nanowire segment, which we could understand using a simple model based on Andreev bound states. Our results show that these built-in barriers are promising as future spectroscopic tools.