ORCID

0000-0003-4690-7882

Date of Award

5-9-2024

Author's School

Graduate School of Arts and Sciences

Author's Department

Physics

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Van der Waals (vdW) heterostructures represent a novel class of artificial materials created by layering atomically thin planar crystals and offer a promising platform for band structure engineering. Here, we focus on a vdW heterostructure of monolayer graphene (G) coupled to a hexagonal boron nitride (h-BN). We utilize cyclotron resonance (CR) spectroscopy as a primary investigative tool for probing the interacting Dirac fermions in graphene. This work presents a system capable of conducting broadband far- to mid-infrared CR spectroscopy in high magnetic fields and ultra-low temperatures. Our study investigates the influence of the h-BN substrate on the properties of graphene in two key aspects. First, the atomic-scale modulations break the local symmetry between the graphene sublattices, influenced by the potential difference between boron and nitrogen atoms in h-BN. We perform CR measurements on high-quality graphene devices, presenting the first observation of the complete lifting of the four-fold degeneracy of Landau levels (LLs) due to broken spin and valley symmetries. Secondly, we explore the effect of near-perfect alignment between G/h- BN that causes the superlattice potential to match the magnetic length scale in graphene, yielding a self-similar energy spectrum. We spectroscopically investigate the fractal levels by measuring optical transitions across the reconstructed LLs in G/h-BN moiré superlattice.

Language

English (en)

Chair and Committee

Erik Henriksen

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