Fabry-P\'erot resonances and a crossover to the quantum Hall regime in ballistic graphene quantum point contacts

TL;DR

This paper demonstrates quantum transport phenomena in a graphene quantum point contact, observing Fabry-Pérot resonances at low magnetic fields and a crossover to quantum Hall effects at high fields, highlighting quantum coherence at elevated temperatures.

Contribution

It reports the first observation of a crossover from Fabry-Pérot to quantum Hall regimes in ballistic graphene QPCs, revealing quantum coherence effects up to tens of kelvins.

Findings

Fabry-Pérot resonances observed at low magnetic fields.

Crossover to quantum Hall regime with high magnetic fields.

Quantum coherence effects persist up to tens of kelvins.

Abstract

We report on the observation of quantum transport and interference in a graphene device that is attached with a pair of split gates to form an electrostatically-defined quantum point contact (QPC). In the low magnetic field regime, the resistance exhibited Fabry-P\'erot (FP) resonances due to np'n (pn'p) cavities formed by the top gate. In the quantum Hall (QH) regime with a high magnetic field, the edge states governed the phenomena, presenting a unique condition where the edge channels of electrons and holes along a p-n junction acted as a solid-state analogue of a monochromatic light beam. We observed a crossover from the FP to QH regimes in ballistic graphene QPC under a magnetic field with varying temperatures. In particular, the collapse of the QH effect was elucidated as the magnetic field was decreased. Our high-mobility graphene device enabled observation of such quantum coherence effects up to several tens of kelvins. The presented device could serve as one of the key elements in future electronic quantum optic devices.