Atomic resolution imaging of the two-component Dirac-Landau levels in a gapped graphene monolayer

TL;DR

This study uses atomic-resolution scanning tunnelling microscopy to directly image and characterize the two-component wavefunction structure of Dirac-Landau levels in a gapped graphene monolayer, revealing the internal spinor structure.

Contribution

First atomic-resolution imaging of the two-component Dirac-Landau levels in gapped graphene, demonstrating the wavefunction amplitude distribution on A and B sublattices.

Findings

Observation of a 20 meV gap due to substrate-induced inversion symmetry breaking

Splitting of the n=0 Landau level into 0+ and 0- levels

Wavefunction amplitude mainly at A sites for 0- and B sites for 0+ Landau levels

Abstract

The wavefunction of massless Dirac fermions is a two-component spinor. In graphene, a one-atom-thick film showing two-dimensional Dirac-like electronic excitations, the two-component representation reflects the amplitude of the electron wavefunction on the A and B sublattices. This unique property provides unprecedented opportunities to image the two components of massless Dirac fermions spatially. Here we report atomic resolution imaging of the two-component Dirac-Landau levels in a gapped graphene monolayer by scanning tunnelling microscopy and spectroscopy. A gap of about 20 meV, driven by inversion symmetry breaking by the substrate potential, is observed in the graphene on both SiC and graphite substrates. Such a gap splits the n = 0 Landau level (LL) into two levels, 0+ and 0-. We demonstrate that the amplitude of the wavefunction of the 0- LL is mainly at the A sites and that of the 0+ LL is mainly at the B sites of graphene, characterizing the internal structure of the spinor of the n = 0 LL. This provides direct evidence of the two-component nature of massless Dirac fermions.