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

Abstract

The wave function of 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 wave function on the $A$ and $B$ sublattices. This unique property provides unprecedented opportunities to image the two components of Dirac fermions spatially. Here, we report atomic resolution imaging of two-component Dirac-Landau levels in gapped graphene monolayers by scanning tunneling microscopy and spectroscopy. A gap of about 20 meV, driven by inversion symmetry breaking by the substrate potential, is observed in the graphene sheets on both SiC and graphite substrates. Such a gap splits the $n=0$ Landau level (LL) into two levels, ${0}_{+}$ and ${0}_{\ensuremath{-}}$. We demonstrate that the amplitude of the wave function of the ${0}_{+}$ LL is mainly on the $A$ sites and that of the ${0}_{\ensuremath{-}}$ LL is mainly on 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 Dirac fermions.