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 $u$= $10^8$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 ${\cal N}=4$ SUSY nonlinear sigma model whose target space is $T^*(CP^{N-1})$ (the cotangent bundle of $CP^{N-1}$) to higher orders in the 1/N expansion. We calculate the $\beta$-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