Transport and quantum coherence in graphene rings: Aharonov-Bohm oscillations, Klein tunneling and particle localization

TL;DR

This paper explores quantum transport in graphene rings, demonstrating how magnetic fields, electrostatic potentials, and disorder influence phenomena like Aharonov-Bohm oscillations, Klein tunneling, and particle localization.

Contribution

It provides a comprehensive simulation of quantum coherence effects in graphene rings, highlighting the interplay of magnetic flux, electrostatic barriers, and disorder on transport phenomena.

Findings

Aharonov-Bohm oscillations observed with magnetic flux.

Klein tunneling affects conductance depending on barrier smoothness.

Disorder induces particle localization, suppressing quantum effects.

Abstract

Simulating quantum transport through mesoscopic, ring-shaped graphene structures, we address various quantum coherence and interference phenomena. First, a perpendicular magnetic field, penetrating the graphene ring, gives rise to Aharonov-Bohm oscillations in the conductance as a function of the magnetic flux, on top of the universal conductance fluctuations. At very high fluxes the interference gets suppressed and quantum Hall edge channels develop. Second, applying an electrostatic potential to one of the ring arms, $nn'n$- or $npn$-junctions can be realized with particle transmission due to normal tunneling or Klein tunneling. In the latter case the Aharonov-Bohm oscillations weaken for smooth barriers. Third, if potential disorder comes in to play, both Aharonov-Bohm and Klein tunneling effects rate down, up to the point where particle localization sets in.