3 research outputs found
Gate-induced magneto-oscillation phase anomalies in graphene bilayers
The magneto-oscillations in graphene bilayers are studied in the vicinity of
the K and K' points of the Brillouin zone within the four-band continuum model
ased on the simplest tight-binding approximation involving only the nearest
neighbor interactions. The model is employed to construct Landau plots for a
variety of carrier concentrations and bias strengths between the graphene
planes. The quantum-mechanical and quasiclassical approaches are compared. We
found that the quantum magneto-oscillations are only asymptotically periodic
and reach the frequencies predicted quasiclassically for high indices of Landau
levels. In unbiased bilayers the phase of oscillations is equal to the phase of
massive fermions. Anomalous behavior of oscillation phases was found in biased
bilayers with broken inversion symmetry. The oscillation frequencies again tend
to quasiclassically predicted ones, which are the same for and , but
the quantum approach yields the gate-tunable corrections to oscillation phases,
which differ in sign for K and K'. These valley-dependent phase corrections
give rise, instead of a single quasiclassical series of oscillations, to two
series with the same frequency but shifted in phase.Comment: 8 pages, 8 figure
Dirac Spectrum in Piecewise Constant One-Dimensional Potentials
We study the electronic states of graphene in piecewise constant potentials
using the continuum Dirac equation appropriate at low energies, and a transfer
matrix method. For superlattice potentials, we identify patterns of induced
Dirac points which are present throughout the band structure, and verify for
the special case of a particle-hole symmetric potential their presence at zero
energy. We also consider the cases of a single trench and a p-n junction
embedded in neutral graphene, which are shown to support confined states. An
analysis of conductance across these structures demonstrates that these
confined states create quantum interference effects which evidence their
presence.Comment: 10 pages, 12 figures, additional references adde
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic