Peculiar Nature of Snake States in Graphene

We study the dynamics of the electrons in a non-uniform magnetic field applied perpendicular to a graphene sheet in the low energy limit when the excitation states can be described by a Dirac type Hamiltonian. We show that as compared to the two-dimensional electron gas (2DEG) snake states in graphene exibit peculiar properties related to the underlying dynamics of the Dirac fermions. The current carried by snake states is locally uncompensated even if the Fermi energy lies between the first non-zero energy Landau levels of the conduction and valence bands. The nature of these states is studied by calculating the current density distribution. It is shown that besides the snake states in finite samples surface states also exist.Comment: 4 pages, 5 figure

Quantum-to-classical crossover of mesoscopic conductance fluctuations

We calculate the system-size-over-wave-length ($M$) dependence of sample-to-sample conductance fluctuations, using the open kicked rotator to model chaotic scattering in a ballistic quantum dot coupled by two $N$-mode point contacts to electron reservoirs. Both a fully quantum mechanical and a semiclassical calculation are presented, and found to be in good agreement. The mean squared conductance fluctuations reach the universal quantum limit of random-matrix-theory for small systems. For large systems they increase $\propto M^2$ at fixed mean dwell time $\tau_D \propto M/N$. The universal quantum fluctuations dominate over the nonuniversal classical fluctuations if $N < \sqrt{M}$. When expressed as a ratio of time scales, the quantum-to-classical crossover is governed by the ratio of Ehrenfest time and ergodic time.Comment: 5 pages, 5 figures: one figure added, references update

Delta excitation in K^+-nucleus collisions

We present calculations for \Delta excitation in the (K^+,K^+) reaction in nuclei. The background from quasielastic K^+ scattering in the \Delta region is also evaluated and shown to be quite small in some kinematical regions, so as to allow for a clean identification of the \Delta excitation strength. Nuclear effects tied to the \Delta renormalization in the nucleus are considered and the reaction is shown to provide new elements to enrich our knowledge of the \Delta properties in a nuclear medium.Comment: 11 pages, 6 figures, LaTe

Backward pion-nucleon scattering

A global analysis of the world data on differential cross sections and polarization asymmetries of backward pion-nucleon scattering for invariant collision energies above 3 GeV is performed in a Regge model. Including the $N_\alpha$, $N_\gamma$, $\Delta_\delta$ and $\Delta_\beta$ trajectories, we reproduce both angular distributions and polarization data for small values of the Mandelstam variable $u$, in contrast to previous analyses. The model amplitude is used to obtain evidence for baryon resonances with mass below 3 GeV. Our analysis suggests a $G_{39}$ resonance with a mass of 2.83 GeV as member of the $\Delta_{\beta}$ trajectory from the corresponding Chew-Frautschi plot.Comment: 12 pages, 16 figure

The 3^3He(e, e′'d)p Reaction in qω\omega-constant Kinematics

The cross section for the $^3$He(e, e$'$d)p reaction has been measured as a function of the missing momentum $p_m$ in q$\omega$ -constant kinematics at beam energies of 370 and 576 MeV for values of the three-momentum transfer $q$ of 412, 504 and 604 \mevc. The L(+TT), T and LT structure functions have been separated for $q$ = 412 and 504 \mevc. The data are compared to three-body Faddeev calculations, including meson-exchange currents (MEC), and to calculations based on a covariant diagrammatic expansion. The influence of final-state interactions and meson-exchange currents is discussed. The $p_m$-dependence of the data is reasonably well described by all calculations. However, the most advanced Faddeev calculations, which employ the AV18 nucleon-nucleon interaction and include MEC, overestimate the measured cross sections, especially the longitudinal part, and at the larger values of $q$. The diagrammatic approach gives a fair description of the cross section, but under(over)estimates the longitudinal (transverse) structure function.Comment: 17 pages, 7 figure

Signatures for short-range correlations in {16}O, observed in the reaction {16}O(e,e'pp){14}C.

The reaction O-16(e,e'pp)C-14 has been studied at a transferred four-momentum (omega,\q\) = (210 MeV, 300 MeV/c). The differential cross sections for the transitions to the ground state and the lowest excited states in C-14 were determined as a function of the momentum of the recoiling C-14 nucleus and the angle between the momentum of the proton emitted in the forward direction and the momentum transfer q. A comparison of the data to the results of calculations, performed with a microscopic model, shows clear signatures for short-range correlations in the O-16 ground state