Sharp Landau Levels in Scanning Tunneling Spectroscopy of Epitaxial Graphene on SiC(000 -1)

Monolayer graphene has unique electronic properties stemming from a low-energy band structure that is linear, with chiral Dirac quasiparticles. In a magnetic field, the Landau level (LL) energies for graphene $E_n$ vary proportional to $\sqrt{nB}$, where $n$ is the LL index. Conversely, Bernal-stacked bilayer graphene and graphite have parabolic dispersion at low energies, resulting in $E_n \propto B$. In this talk we measure the LL spectrum of the top graphene layer directly via scanning tunneling spectroscopy (STS) at a 4.3 K. We show that for $\approx 10$-layer epitaxial graphene grown on SiC(000 -1), the spectrum exhibits very sharp peaks (including a strong n=0 peak) spaced as $E_n \propto \sqrt{nB}$. This spectrum indicates that the rotational stacking in multilayer epitaxial graphene effectively decouples the layers, producing single-layer graphene behavior. Work supported in part by NSF, NRI-INDEX, and the W. M. Keck Foundation.