title: Single-layer behavior and its breakdown in twisted graphene layers.
abstract: 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° the low energy carriers exhibit Landau level spectra characteristic of massless Dirac fermions. Above 20° the layers effectively decouple and the electronic properties are indistinguishable from those in single-layer graphene, while for smaller angles we observe a slowdown 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.
authors.affiliation: Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08855, USA.
authors.forename: A
authors.initials: A
authors.lastname: Luican
authors.forename: Guohong
authors.initials: G
authors.lastname: Li
authors.forename: A
authors.initials: A
authors.lastname: Reina
authors.forename: J
authors.initials: J
authors.lastname: Kong
authors.forename: R R
authors.initials: RR
authors.lastname: Nair
authors.forename: K S
authors.initials: KS
authors.lastname: Novoselov
authors.forename: A K
authors.initials: AK
authors.lastname: Geim
authors.forename: E Y
authors.initials: EY
authors.lastname: Andrei