Geometry effects in topologically confined bilayer graphene loops

TL;DR

This paper explores how the shape and size of topological loops in bilayer graphene influence electronic confinement, zero-energy states, and magnetic field effects, revealing shape-dependent spectral patterns and valley splittings.

Contribution

It demonstrates the impact of loop geometry on electronic states in bilayer graphene, including shape-dependent spectra and magnetic field-induced phenomena.

Findings

Large loops follow a perimeter-based quantization rule.

Small loops show shape-dependent spectral features.

Magnetic fields induce valley splittings and persistent currents.

Abstract

We investigate the electronic confinement in bilayer graphene by topological loops of different shapes. These loops are created by lateral gates acting via gap inversion on the two graphene sheets. For large-area loops the spectrum is well described by a quantization rule depending only on the loop perimeter. For small sizes, the spectrum depends on the loop shape. We find that zero-energy states exhibit a characteristic pattern that strongly depends on the spatial symmetry. We show this by considering loops of higher to lower symmetry (circle, square, rectangle and irregular polygon). Interestingly, magnetic field causes valley splittings of the states, an asymmetry between energy reversal states, flux periodicities and the emergence of persistent currents.