Abstract
Phys. Rev. Lett. 106, 126802 (2011) We report high magnetic field scanning tunneling microscopy and Landau level
spectroscopy of twisted graphene layers grown by chemical vapor deposition. For
twist angles exceeding ~3 degrees the low energy carriers exhibit Landau level
spectra characteristic of massless Dirac fermions. Above 20 degrees the layers
effectively decouple and the electronic properties are indistinguishable from
those in single layer graphene, while for smaller angles we observe a slow-down
of the carrier velocity which is strongly angle dependent. At the smallest
angles the spectra are dominated by twist induced Van Hove singularities and
the Dirac fermions eventually become localized. An unexpected electron-hole
asymmetry is observed which is substantially larger than the asymmetry in
either single or untwisted bilayer graphene.