Kavli Affiliate: Joseph Falson
| First 5 Authors: Yusuke Kozuka, Atsushi Sakaguchi, Joseph Falson, Atsushi Tsukazaki, Masashi Kawasaki
| Summary:
Quantum Hall/superconductor junctions have been an attractive topic as the
two macroscopically quantum states join at the interface. Despite longstanding
efforts, however, experimental understanding of this system has not been
settled yet. One of the reasons is that most semiconductors hosting
high-mobility two-dimensional electron systems (2DES) usually form Schottky
barriers at the metal contacts, preventing efficient proximity between the
quantum Hall edge states and Cooper pairs. Only recently have relatively
transparent 2DES/superconductor junctions been investigated in graphene. In
this study, we propose another material system for investigating
2DES/superconductor junctions, that is ZnO-based heterostrcuture. Due to the
ionic nature of ZnO, a Schottky barrier is not effectively formed at the
contact with a superconductor MoGe, as evidenced by the appearance of Andreev
reflection at low temperatures. With applying magnetic field, while clear
quantum Hall effect is observed for ZnO 2DES, conductance across the junction
oscillates with the filling factor of the quantum Hall states. We find that
Andreev reflection is suppressed in the well developed quantum Hall regimes,
which we interpret as a result of equal probabilities of normal and Andreev
reflections as a result of multiple Andreev reflection at the
2DES/superconductor interface.
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