Electronic Mach-Zehnder interference in a bipolar hybrid monolayer-bilayer graphene junction

TL;DR

This paper demonstrates valley-polarized electron interference in a bipolar monolayer-bilayer graphene junction, enabling a tunable Mach-Zehnder interferometer, with conductance oscillations influenced by edge termination and magnetic field.

Contribution

It introduces a valley-polarized Mach-Zehnder interferometer in monolayer-bilayer graphene junctions and analyzes edge effects on quantum Hall interference patterns.

Findings

Valley-polarized edge-channel interference observed.

Conductance oscillations range from 0 to 2e^2/h.

Edge termination significantly affects interference patterns.

Abstract

Graphene matter in a strong magnetic field, realizing one-dimensional quantum Hall channels, provides a unique platform for studying electron interference. Here, using the Landauer-B\"uttiker formalism along with the tight-binding model, we investigate the quantum Hall (QH) effects in unipolar and bipolar monolayer-bilayer graphene (MLG-BLG) junctions. We find that a Hall bar made of an armchair MLG-BLG junction in the bipolar regime results in valley-polarized edge-channel interferences and can operate a fully tunable Mach-Zehnder (MZ) interferometer device. Investigation of the bar-width and magnetic-field dependence of the conductance oscillations shows that the MZ interference in such structures can be drastically affected by the type of (zigzag) edge termination of the second layer in the BLG region [composed of vertical dimer or non-dimer atoms]. Our findings reveal that both interfaces exhibit a double set of Aharonov-Bohm interferences, with the one between two oppositely valley-polarized edge channels dominating and causing a large-amplitude conductance oscillation ranging from 0 to $ 2 e^2 / h$. We explain and analyze our findings by analytically solving the Dirac-Weyl equation for a gated semi-infinite MLG-BLG junction.