10,190 research outputs found
Energy-Momentum dispersion relation of plasmarons in bilayer graphene
The relation between the energy and momentum of plasmarons in bilayer
graphene is investigated within the Overhauser approach, where the
electron-plasmon interaction is described as a field theoretical problem. We
find that the Dirac-like spectrum is shifted by depending on the electron concentration and
electron momentum. The shift increases with electron concentration as the
energy of plasmons becomes larger. The dispersion of plasmarons is more
pronounced than in the case of single layer graphene, which is explained by the
fact that the energy dispersion of electrons is quadratic and not linear. We
expect that these predictions can be verified using angle-resolved
photoemission spectroscopy (ARPES).Comment: 4 pages, 3 figure
Characterization of the size and position of electron-hole puddles at a graphene p-n junction
The effect of an electron-hole puddle on the electrical transport when
governed by snake states in a bipolar graphene structure is investigated. Using
numerical simulations we show that information on the size and position of the
electron-hole puddle can be obtained using the dependence of the conductance on
magnetic field and electron density of the gated region. The presence of the
scatterer disrupts snake state transport which alters the conduction pattern.
We obtain a simple analytical formula that connects the position of the
electron-hole puddle with features observed in the conductance. Size of the
electron-hole puddle is estimated from the magnetic field and gate potential
that maximizes the effect of the puddle on the electrical transport.Comment: This is an author-created, un-copyedited version of an article
published in Nanotechnology. IOP Publishing Ltd is not responsible for any
errors or omissions in this version of the manuscript or any version derived
from it. The Version of Record is available online at
doi:10.1088/0957-4484/27/10/10520
Magneto-optical transport properties of monolayer phosphorene
The electronic properties of monolayer phosphorene are exotic due to its
puckered structure and large intrinsic direct band gap. We derive and discuss
its band structure in the presence of a perpendicular magnetic field. Further,
we evaluate the magneto-optical Hall and longitudinal optical conductivities,
as functions of temperature, magnetic field, and Fermi energy, and show that
they are strongly influenced by the magnetic field. The imaginary part of the
former and the real part of the latter exhibit regular {\it interband}
oscillations as functions of the frequency in the range
eV. Strong {\it intraband} responses in the latter
and week ones in the former occur at much lower frequencies. The
magneto-optical response can be tuned in the microwave-to-terahertz and visible
frequency ranges in contrast with a conventional two-dimensional electron gas
or graphene in which the response is limited to the terahertz regime. This
ability to isolate carriers in an anisotropic structure may make phosphorene a
promising candidate for new optical devices.Comment: 7 pages and 8 figure
Single-layer and bilayer graphene superlattices: collimation, additional Dirac points and Dirac lines
We review the energy spectrum and transport properties of several types of
one- dimensional superlattices (SLs) on single-layer and bilayer graphene. In
single-layer graphene, for certain SL parameters an electron beam incident on a
SL is highly collimated. On the other hand there are extra Dirac points
generated for other SL parameters. Using rectangular barriers allows us to find
analytic expressions for the location of new Dirac points in the spectrum and
for the renormalization of the electron velocities. The influence of these
extra Dirac points on the conductivity is investigated. In the limit of
{\delta}-function barriers, the transmission T through, conductance G of a
finite number of barriers as well as the energy spectra of SLs are periodic
functions of the dimensionless strength P of the barriers, P{\delta}(x) ~ V
(x). For a Kronig-Penney SL with alternating sign of the height of the barriers
the Dirac point becomes a Dirac line for P = {\pi}/2 + n{\pi} with n an
integer. In bilayer graphene, with an appropriate bias applied to the barriers
and wells, we show that several new types of SLs are produced and two of them
are similar to type I and type II semiconductor SLs. Similar as in single-layer
graphene extra "Dirac" points are found. Non-ballistic transport is also
considered.Comment: 26 pages, 17 figure
Extra Dirac points in the energy spectrum for superlattices on single-layer graphene
We investigate the emergence of extra Dirac points in the electronic
structure of a periodically spaced barrier system, i.e., a superlattice, on
single-layer graphene, using a Dirac-type Hamiltonian. Using square barriers
allows us to find analytic expressions for the occurrence and location of these
new Dirac points in k-space and for the renormalization of the electron
velocity near them in the low-energy range. In the general case of unequal
barrier and well widths the new Dirac points move away from the Fermi level and
for given heights of the potential barriers there is a minimum and maximum
barrier width outside of which the new Dirac points disappear. The effect of
these extra Dirac points on the density of states and on the conductivity is
investigated.Comment: 7 pages, 8 figures, accepted for publication in Phys. Rev.
Ballistic spin transport through electronic stub tuners: spin precession, selection, and square-wave transmission
Ballistic spin transport is studied through electronic tuners with double
stubs attached to them. The spins precess due to the spin-orbit interaction.
Injected polarized spins can exit the structure polarized in the opposite
direction. A nearly square-wave spin transmission, with values 1 and 0, can be
obtained using a periodic system of symmetric stubs and changing their length
or width. The gaps in the transmission can be widened using asymmetric stubs.
An additional modulation is obtained upon combining stub structures with
different values of the spin-orbit strength.Comment: 3 pages, 4 figure
Tuning the polarized quantum phonon transmission in graphene nanoribbons
We propose systems that allow a tuning of the phonon transmission function
T() in graphene nanoribbons by using C isotope barriers, antidot
structures, and distinct boundary conditions. Phonon modes are obtained by an
interatomic fifth-nearest neighbor force-constant model (5NNFCM) and
T() is calculated using the non-equilibrium Green's function formalism.
We show that by imposing partial fixed boundary conditions it is possible to
restrict contributions of the in-plane phonon modes to T() at low
energy. On the contrary, the transmission functions of out-of-plane phonon
modes can be diminished by proper antidot or isotope arrangements. In
particular, we show that a periodic array of them leads to sharp dips in the
transmission function at certain frequencies which can be
pre-defined as desired by controlling their relative distance and size. With
this, we demonstrated that by adequate engineering it is possible to govern the
magnitude of the ballistic transmission functions T in graphene
nanoribbons. We discuss the implications of these results in the design of
controlled thermal transport at the nanoscale as well as in the enhancement of
thermo-electric features of graphene-based materials
Double quantum dots defined in bilayer graphene
Artificial molecular states of double quantum dots defined in bilayer
graphene are studied with the atomistic tight-binding and its low-energy
continuum approximation. We indicate that the extended electron wave functions
have opposite parities on each of the sublattices at both graphene layers and
that the ground-state wave function components change from bonding to
antibonding with the interdot distance. In the weak coupling limit -- the most
relevant for the quantum dots defined electrostatically -- the signatures of
the interdot coupling include -- for the two-electron ground state -- formation
of states with symmetric or antisymmetric spatial wave functions split by the
exchange energy. In the high energy part of the spectrum the states with both
electrons in the same dot are found with the splitting of energy levels
corresponding to simultaneous tunneling of the electron pair from one dot to
the other
Homotopy Methods to Compute Equilibria in Game Theory
This paper presents a complete survey of the use of homotopy methods in game theory.Homotopies allow for a robust computation of game-theoretic equilibria and their refinements. Homotopies are also suitable to compute equilibria that are selected by variousselection theories. We present all relevant techniques underlying homotopy algorithms.We give detailed expositions of the Lemke-Howson algorithm and the Van den Elzen-Talman algorithm to compute Nash equilibria in 2-person games, and the Herings-Vanden Elzen, Herings-Peeters, and McKelvey-Palfrey algorithms to compute Nash equilibriain general n-person games.operations research and management science;
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