Imaging Quantum Interference in Stadium-Shaped Monolayer and Bilayer Graphene Quantum Dots

TL;DR

This study fabricates and visualizes stadium-shaped graphene quantum dots in monolayer and bilayer forms, revealing the impact of confinement properties on quantum chaos signatures, with implications for quantum device design.

Contribution

It demonstrates the creation and direct imaging of stadium-shaped graphene quantum dots and analyzes how confinement affects quantum chaos signatures in these systems.

Findings

Monolayer graphene QDs lack clear quantum chaos signatures due to leaky confinement.

Bilayer graphene QDs show stronger confinement but still do not exhibit quantum chaos signatures.

Visualization aligns with tight-binding simulations, clarifying the role of confinement in quantum chaos.

Abstract

Experimental realization of graphene-based stadium-shaped quantum dots (QDs) have been few and incompatible with scanned probe microscopy. Yet, direct visualization of electronic states within these QDs is crucial for determining the existence of quantum chaos in these systems. We report the fabrication and characterization of electrostatically defined stadium-shaped QDs in heterostructure devices composed of monolayer graphene (MLG) and bilayer graphene (BLG). To realize a stadium-shaped QD, we utilized the tip of a scanning tunneling microscope to charge defects in a supporting hexagonal boron nitride flake. The stadium states visualized are consistent with tight-binding-based simulations, but lack clear quantum chaos signatures. The absence of quantum chaos features in MLG-based stadium QDs is attributed to the leaky nature of the confinement potential due to Klein tunneling. In contrast, for BLG-based stadium QDs (which have stronger confinement) quantum chaos is precluded by the smooth confinement potential which reduces interference and mixing between states.