Particle creation by moving spherical shell in the dynamical Casimir effect

The creation of massless scalar particles from the quantum vacuum by spherical shell with time varying radius is studied. In the general case of motion the equations are derived for the instantaneous basis expansion coefficients. The examples are considered when the mean number of particles can be explicitly evaluated in the adiabatic approximation.Comment: 9 pages, LaTeX, no figures, typos corrected, discussion added. Journal-ref adde

Wigner Molecules in Nanostructures

The one-- and two-- particle densities of up to four interacting electrons with spin, confined within a quasi one--dimensional ``quantum dot'' are calculated by numerical diagonalization. The transition from a dense homogeneous charge distribution to a dilute localized Wigner--type electron arrangement is investigated. The influence of the long range part of the Coulomb interaction is studied. When the interaction is exponentially cut off the ``crystallized'' Wigner molecule is destroyed in favor of an inhomogeneous charge distribution similar to a charge density wave .Comment: 10 pages (excl. Figures), Figures available on request LaTe

Signatures of electron correlations in the transport properties of quantum dots

The transition matrix elements between the correlated $N$ and $N\!+\!1$ electron states of a quantum dot are calculated by numerical diagonalization. They are the central ingredient for the linear and non--linear transport properties which we compute using a rate equation. The experimentally observed variations in the heights of the linear conductance peaks can be explained. The knowledge of the matrix elements as well as the stationary populations of the states allows to assign the features observed in the non--linear transport spectroscopy to certain transition and contains valuable information about the correlated electron states.Comment: 4 pages (revtex,27kB) + 3 figures in one file ziped and uuencoded (postscript,33kB), to appear in Phys.Rev.B as Rapid Communicatio

Particle creation in an oscillating spherical cavity

We study the creation of massless scalar particles from the quantum vacuum due to the dynamical Casimir effect by spherical shell with oscillating radius. In the case of a small amplitude of the oscillation, to solve the infinite set of coupled differential equations for the instantaneous basis expansion coefficients we use the method based on the time-dependent perturbation theory of the quantum mechanics. To the first order of the amplitude we derive the expressions for the number of the created particles for both parametric resonance and non-resonance cases.Comment: 8 pages, LaTeX, no figure

Effect of oxygen plasma etching on graphene studied with Raman spectroscopy and electronic transport

We report a study of graphene and graphene field effect devices after exposure to a series of short pulses of oxygen plasma. We present data from Raman spectroscopy, back-gated field-effect and magneto-transport measurements. The intensity ratio between Raman "D" and "G" peaks, I(D)/I(G) (commonly used to characterize disorder in graphene) is observed to increase approximately linearly with the number (N(e)) of plasma etching pulses initially, but then decreases at higher Ne. We also discuss implications of our data for extracting graphene crystalline domain sizes from I(D)/I(G). At the highest Ne measured, the "2D" peak is found to be nearly suppressed while the "D" peak is still prominent. Electronic transport measurements in plasma-etched graphene show an up-shifting of the Dirac point, indicating hole doping. We also characterize mobility, quantum Hall states, weak localization and various scattering lengths in a moderately etched sample. Our findings are valuable for understanding the effects of plasma etching on graphene and the physics of disordered graphene through artificially generated defects.Comment: 10 pages, 5 figure

Transport properties of quantum dots in the Wigner molecule regime

The transport properties of quantum dots with up to N=7 electrons ranging from the weak to the strong interacting regime are investigated via the projected Hartree-Fock technique. As interactions increase radial order develops in the dot, with the formation of ring and centered-ring structures. Subsequently, angular correlations appear, signalling the formation of a Wigner molecule state. We show striking signatures of the emergence of Wigner molecules, detected in transport. In the linear regime, conductance is exponentially suppressed as the interaction strength grows. A further suppression is observed when centered-ring structures develop, or peculiar spin textures appear. In the nonlinear regime, the formation of molecular states may even lead to a conductance enhancement.Comment: 26 pages, 14 figures, Accepted for publication on New Journal of Physic

Angular dependence of novel magnetic quantum oscillations in a quasi-two-dimensional multiband Fermi liquid with impurities

The semiclassical Lifshitz-Kosevich-type description is given for the angular dependence of quantum oscillations with combination frequencies in a multiband quasi-two-dimensional Fermi liquid with a constant number of electrons. The analytical expressions are found for the Dingle, thermal, spin, and amplitude (Yamaji) reduction factors of the novel combination harmonics, where the latter two strongly oscillate with the direction of the field. At the "magic" angles those factors reduce to the purely two-dimensional expressions given earlier. The combination harmonics are suppressed in the presence of the non-quantized ("background") states, and they decay exponentially faster with temperature and/or disorder compared to the standard harmonics, providing an additional tool for electronic structure determination. The theory is applied to Sr$_2$RuO$_4$.Comment: 5 pages, 2 figures, minor typos correcte