1,495 research outputs found
One-dimensional semirelativity for electrons in carbon nanotubes
It is shown that the band structure of single-wall semiconducting carbon
nanotubes (CNT) is analogous to relativistic description of electrons in
vacuum, with the maximum velocity = cm/s replacing the light velocity.
One-dimensional semirelativistic kinematics and dynamics of electrons in CNT is
formulated. Two-band k.p Hamiltonian is employed to demonstrate that electrons
in CNT experience a Zitterbewegung (trembling motion) in absence of external
fields. This Zitterbewegung should be observable much more easily in CNT than
its analogue for free relativistic electrons in vacuum.Comment: 4 pages no figure
Low frequency Rabi spectroscopy for a dissipative two-level system
We have analyzed the interaction of a dissipative two level quantum system
with high and low frequency excitation. The system is continuously and
simultaneously irradiated by these two waves. If the frequency of the first
signal is close to the level separation the response of the system exhibits
undamped low frequency oscillations whose amplitude has a clear resonance at
the Rabi frequency with the width being dependent on the damping rates of the
system. The method can be useful for low frequency Rabi spectroscopy in various
physical systems which are described by a two level Hamiltonian, such as nuclei
spins in NMR, double well quantum dots, superconducting flux and charge qubits,
etc. As the examples, the application of the method to a nuclear spin and to
the readout of a flux qubit are briefly discussed.Comment: 4 pages, 3 figures, the figures are modifie
Superlattice properties of carbon nanotubes in a transverse electric field
Electron motion in a (n,1) carbon nanotube is shown to correspond to a de
Broglie wave propagating along a helical line on the nanotube wall. This
helical motion leads to periodicity of the electron potential energy in the
presence of an electric field normal to the nanotube axis. The period of this
potential is proportional to the nanotube radius and is greater than the
interatomic distance in the nanotube. As a result, the behavior of an electron
in a (n,1) nanotube subject to a transverse electric field is similar to that
in a semiconductor superlattice. In particular, Bragg scattering of electrons
from the long-range periodic potential results in the opening of gaps in the
energy spectrum of the nanotube. Modification of the bandstructure is shown to
be significant for experimentally attainable electric fields, which raises the
possibility of applying this effect to novel nanoelectronic devices.Comment: 7 pages, 3 figure
Cancellation of UV Divergences in the N=4 SUSY Nonlinear Sigma Model in Three Dimensions
We study the UV properties of the three-dimensional SUSY
nonlinear sigma model whose target space is (the cotangent
bundle of ) to higher orders in the 1/N expansion. We calculate the
-function to next-to-leading order and verify that it has no quantum
corrections at leading and next-to-leading orders.Comment: 10 pages, 2 figures. references adde
Excitons in narrow-gap carbon nanotubes
We calculate the exciton binding energy in single-walled carbon nanotubes
with narrow band gaps, accounting for the quasi-relativistic dispersion of
electrons and holes. Exact analytical solutions of the quantum relativistic
two-body problem are obtain for several limiting cases. We show that the
binding energy scales with the band gap, and conclude on the basis of the data
available for semiconductor nanotubes that there is no transition to an
excitonic insulator in quasi-metallic nanotubes and that their THz applications
are feasible.Comment: 11 pages, 3 figures. Several references and an additional appendix
adde
Mycalolide-B, a novel and specific inhibitor of actomyosin ATPase isolated from marine sponge
AbstractA toxin isolated from marine sponge, mycalolide-B, inhibited smooth muscle contractions without changing cytosolic Ca2+ levels. It also inhibited Ca2+-induced contraction in permeabilized smooth muscles. In native actomyosin prepared from chicken gizzard, mycalolide-B inhibited superprecipitation and Mg2+-ATPase activity stimulated by Ca2+ without changing myosin light chain phosphorylation. In the permeabilized muscle and native actomyosin preparation thiophosphorylated with ATPγS, mycalolide-B inhibited ATP-induced contraction and Mg2+-ATPase activity, respectively, in the absence of Ca2+. Mycalolide-B also inhibited Mg2+-ATPase activity of skeletal muscle native actomyosin. Mycalolide-B had no effect on calmodulin-stimulated (Ca2+Mg2+)-ATPase activity of erythrocyte membranes. These results suggest that mycalolide-B selectively inhibits actin—myosin interaction
Elastic scattering theory and transport in graphene
Electron properties of graphene are described in terms of Dirac fermions.
Here we thoroughly outline the elastic scattering theory for the
two-dimensional massive Dirac fermions in the presence of an axially symmetric
potential. While the massless limit is relevant for pristine graphene, keeping
finite mass allows for generalizations onto situations with broken symmetry
between the two sublattices, and provides a link to the scattering theory of
electrons in a parabolic band. We demonstrate that the Dirac theory requires
short-distance regularization for potentials which are more singular than 1/r.
The formalism is then applied to scattering off a smooth short-ranged
potential. Next we consider the Coulomb potential scattering, where the Dirac
theory is consistent for a point scatterer only for the effective impurity
strength below 1/2. From the scattering phase shifts we obtain the exact
Coulomb transport cross-section in terms of the impurity strength. The results
are relevant for transport in graphene in the presence of impurities that do
not induce scattering between the Dirac points in the Brillouin zone.Comment: 17 pages, 4 figures. Published versio
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