Electronic coherence in nanoscale semiconductor devices

摘要

The application of semiconductor nanostructures to experiments in the coherent quantum regime demands high quality materials and interfaces between device layers. In this talk I will present recent low-temperature transport results on two systems: (ⅰ) core-shell nanowires and (ⅱ) superconductor/semiconductor hybrid structures. The results demonstrate aspects of electronic coherence in very different settings. The InAs-InAlAs core-shell nanowires are desirable for realizing gate-controlled spin qubits, a key ingredient being a core-shell interface free from defects that succeeds in passivating InAs surfaces states. Axial field magnetoconductance measurements reveal periodic oscillations corresponding to a single flux quantum, which we relate to phase coherent electronic states around the nanowire circumference. Remarkably, the signatures of these phase coherent states are observed even in the diffusive transport regime. We have also investigated superconductor/semiconductor junctions with an eventual goal to study topological states relevant to quantum information processing. The device consists of NbN leads deposited onto an InAs two-dimensional electron gas heterostructure. Here we see evidence for proximity effect superconductivity in the junction and Andreev reflection physics. However, no supercurrent is observed at 1.4 K, and experiments at lower temperature and with narrower gap junctions are in progress.