Minimal Single-Particle Hamiltonian for Charge Carriers in Epitaxial Graphene on 4H-SiC(0001)

TL;DR

This paper develops a minimal microscopic Hamiltonian for epitaxial graphene on 4H-SiC(0001), explaining experimental phenomena and predicting energy gaps in nanoribbons, aiding large-scale graphene studies.

Contribution

It introduces a first-principles-based microscopic model Hamiltonian for epitaxial graphene on 4H-SiC(0001), revealing origins of experimental features and predicting energy gaps in nanoribbons.

Findings

Uncovers origins of broken-symmetry states around Dirac points.

Predicts a 0.2 eV energy gap in armchair nanoribbons wider than 15 nm.

Establishes the role of substates in modifying electronic properties.

Abstract

We present a minimal but crucial microscopic theory for epitaxial graphene and graphene nanoribbons on the 4H-SiC(0001) surface -- protopypical materials to explore physical properties of graphene in large scale. Coarse-grained model Hamiltonians are constructed based on the atomic and electronic structures of the systems from first-principles calculations. From the theory, we unambiguously uncover origins of several intriguing experimental observations such as broken-symmetry states around the Dirac points and new energy bands arising throughout the Brillouin zone, thereby establishing the role of substates in modifying electronic properties of graphene. We also predict that armchair graphene nanoribbons on the surface have a single energy gap of 0.2 eV when their widths are over 15 nm, in sharp contrast to their usual family behavior.