Floating up of the zero-energy Landau level in monolayer epitaxial graphene

TL;DR

This study reveals that the zero-energy Landau level in monolayer epitaxial graphene can float above the Fermi energy at low magnetic fields, contrasting with traditional expectations and linked to substrate effects.

Contribution

It demonstrates the magnetic field dependence of the zero-energy Landau level in epitaxial graphene, highlighting substrate-induced symmetry breaking as a key factor.

Findings

Zero-energy Landau level floats above Fermi energy at low B

Substrate-induced symmetry breaking splits zeroth LL degeneracy

Contrasts with behavior in mechanically exfoliated graphene

Abstract

We report on magneto-transport measurements on low-density, large-area monolayer epitaxial graphene devices grown on SiC. We show that the zero-energy Landau level (LL) in monolayer graphene, which is predicted to be magnetic field ($B$)-independent, can float up above the Fermi energy at low $B$. This is supported by the temperature ($T$)-driven flow diagram approximated by the semi-circle law as well as the $T$-independent point in the Hall conductivity $\sigma_{xy}$ near $e^2/h$. Our experimental data are in sharp contrast to conventional understanding of the zeroth LL and metallic-like behavior in pristine graphene prepared by mechanical exfoliation at low $T$. This surprising result can be ascribed to substrate-induced sublattice symmetry breaking which splits the degeneracy of the zeroth Landau level. Our finding provides a unified picture regarding the metallic behavior in pristine graphene prepared by mechanical exfoliation, and the insulating behavior and the insulator-quantum Hall transition in monolayer epitaxial graphene.