Visualization of Strain-Induced Landau Levels in a Graphene - Black Phosphorus Heterostructure

TL;DR

This study demonstrates how stacking graphene on black phosphorus with a specific twist angle induces uniform strain and pseudo magnetic fields, leading to observable Landau levels and flat bands, advancing strain engineering in 2D heterostructures.

Contribution

It introduces nano-ARPES as a tool to directly observe strain-induced Landau levels in graphene/black phosphorus heterostructures, revealing uniform pseudo magnetic fields.

Findings

Observation of flat bands within the Dirac cone.

Detection of a pseudo magnetic field of 11.36 T.

Identification of a 20-degree twist angle in the heterostructure.

Abstract

Strain-induced pseudo magnetic fields offer the possibility of realizing zero magnetic field Quantum Hall effect in graphene, possibly up to room temperature, representing a promising avenue for lossless charge transport applications. Strain engineering on graphene has been achieved via random nanobubbles or artificial nanostructures on the substrate, but the highly localized and non-uniform pseudomagnetic fields can make spectroscopic probes of electronic structure difficult. Heterostructure engineering offers an alternative approach: By stacking graphene on top of another van der Waals material with large lattice mismatch at a desired twist angle, it is possible to generate large strain-induced pseudo magnetic fields uniformly over the entire heterostructure. Here, we report using nano-angle resolved photoemission spectroscopy (nano-ARPES) to probe the electronic bandstructure of a graphene/black phosphorus heterostructure (G/BP). By directly measuring the iso-energy contours of graphene and black phosphorus we determine a twist angle of 20-degrees in our heterostructure. High-resolution nano-ARPES of the graphene bands near the Fermi level reveals the emergence of flat bands located within the Dirac cone. The spacing of the flat bands is consistent with Landau level formation in graphene, and corresponds to a pseudo-field of 11.36 T. Our work provides a new way to study quantum Hall phases induced by strain in 2D materials and heterostructures.