3,592 research outputs found
Ballistic miniband conduction in a graphene superlattice
Rational design of artificial lattices yields effects unavailable in simple
solids, and vertical superlattices of multilayer semiconductors are already
used in optical sensors and emitters. Manufacturing lateral superlattices
remains a much bigger challenge, with new opportunities offered by the use of
moire patterns in van der Waals heterostructures of graphene and hexagonal
crystals such as boron nitride (h-BN). Experiments to date have elucidated the
novel electronic structure of highly aligned graphene/h-BN heterostructures,
where miniband edges and saddle points in the electronic dispersion can be
reached by electrostatic gating. Here we investigate the dynamics of electrons
in moire minibands by transverse electron focusing, a measurement of ballistic
transport between adjacent local contacts in a magnetic field. At low
temperatures, we observe caustics of skipping orbits extending over hundreds of
superlattice periods, reversals of the cyclotron revolution for successive
minibands, and breakdown of cyclotron motion near van Hove singularities. At
high temperatures, we study the suppression of electron focusing by inelastic
scattering
Orbital Magnetism of 2D Chaotic Lattices
We study the orbital magnetism of 2D lattices with chaotic motion of
electrons withing a primitive cell. Using the temperature diagrammatic
technique we evaluate the averaged value and rms fluctuation of magnetic
response in the diffusive regime withing the model of non-interacting
electrons. The fluctuations of magnetic susceptibility turn out to be large and
at low temperature can be of the order of , where
is the Fermi wavevector, is the mean free path, and is
the Landau susceptibility. In the certain region of magnetic fields the
paramagnetic contribution to the averaged response is field independent and
larger than the absolute value of Landau response.Comment: 6 pages, Latex file, figures available upon reques
Time-dependent mode structure for Lyapunov vectors as a collective movement in quasi-one-dimensional systems
Time dependent mode structure for the Lyapunov vectors associated with the
stepwise structure of the Lyapunov spectra and its relation to the momentum
auto-correlation function are discussed in quasi-one-dimensional many-hard-disk
systems. We demonstrate mode structures (Lyapunov modes) for all components of
the Lyapunov vectors, which include the longitudinal and transverse components
of their spatial and momentum parts, and their phase relations are specified.
These mode structures are suggested from the form of the Lyapunov vectors
corresponding to the zero-Lyapunov exponents. Spatial node structures of these
modes are explained by the reflection properties of the hard-walls used in the
models. Our main interest is the time-oscillating behavior of Lyapunov modes.
It is shown that the largest time-oscillating period of the Lyapunov modes is
twice as long as the time-oscillating period of the longitudinal momentum
auto-correlation function. This relation is satisfied irrespective of the
particle number and boundary conditions. A simple explanation for this relation
is given based on the form of the Lyapunov vector.Comment: 39 pages, 21 figures, Manuscript including the figures of better
quality is available from http://www.phys.unsw.edu.au/~gary/Research.htm
An (N-1)-dimensional convex compact set gives an N-dimensional traveling front in the Allen--Cahn equation
This paper studies traveling fronts to the Allen–Cahn equation in RN for N ≥ 3. Let
(N −2)-dimensional smooth surfaces be the boundaries of compact sets in RN−1 and assume that all principal curvatures are positive everywhere. We define an equivalence relation between them and prove that there exists a traveling front associated with a given surface and that it is asymptotically stable for given initial perturbation. The associated traveling fronts coincide up to phase transition if and only if the given surfaces satisfy the equivalence relation
Galaxy Interaction and Starburst-Seyfert Connection
Galaxy interactions are studied in terms of the starburst-Seyfert connection.
The starburst requires a high rate of gas supply. Since the efficiency for
supplying the gas is high in a galaxy interaction, although the companion is
not necessarily discernible, Seyfert galaxies with circumnuclear starbursts are
expected to be interacting. Since the large amounts of circumnuclear gas and
dust obscure the broad-line region, they are expected to be observed as Seyfert
2. The active galactic nucleus itself does not require a high rate of gas
supply. Seyfert galaxies without circumnuclear starbursts are not necessarily
expected to be interacting even at the highest luminosities. They are not
necessarily expected to evolve from Seyfert galaxies with circumnuclear
starbursts. We derive these and other theoretical expectations and confirm them
with statistics on observational data of magnitude-limited samples of Seyfert
galaxies.Comment: 28 pages, to appear in The Astrophysical Journa
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