The coherent propagation of elastic waves in a solid filled with a random distribution of pinned dislocation segments is studied to all orders in perturbation theory. It is shown that, within the independent scattering approximation, the perturbation series that generates the mass operator is a geometric series that can thus be formally summed. A divergent quantity is shown to be renormalizable to zero at low frequencies. At higher frequencies said quantity can be expressed in terms of a cut-off with dimensions of length, related to the dislocation length, and physical quantities can be computed in terms of two parameters, to be determined by experiment. The approach used in this problem is compared and contrasted with the scattering of de Broglie waves by delta-function potentials as described by the Schrödinger equation.
We establish the dominant effect of anisotropic weak localization ͑WL͒ in three dimensions ͑3D͒ associated with a propagative Fermi surface on the conductivity correction in heavily nitrogen-doped ultrananocrystalline diamond ͑UNCD͒ films based on magnetoresistance studies at low temperatures. Also, low-temperature electrical conductivity can show weakly localized transport in 3D combined with the effect of electron-electron interactions in these materials, which is remarkably different from the conductivity in two-dimensional WL or strong localization regime. The corresponding dephasing time of electronic wave functions in these systems described as ϳT −p with p Ͻ 1, follows a relatively weak temperature dependence compared to the generally expected nature for bulk dirty metals having p Ն 1. The temperature dependence of Hall ͑electron͒ mobility together with an enhanced electron density has been used to interpret the unusual magnetotransport features and show delocalized electronic transport in these n-type UNCD films, which can be described as lowdimensional superlattice structures.
We study the diffusion of anti-plane elastic waves in a two dimensional continuum by many, randomly placed, screw dislocations. Building on a previously developed theory for coherent prop-
Abstract. In the framework of strong field QED, the generation of a residual alternating polarization current is demonstrated, which remains after switching off an external field pulse. This effect is stipulated by inertial properties of the physical vacuum. In the standard vacuum D = 2 + 1 QED, this current is rapidly damped fast but can be available, apparently, for observation in the graphene, where the Fermi velocity v F c plays an analogous role as the light velocity.
Resonant tunneling features through impurity clusters embedded in an insulating matrix have been examined through the inter-play between the size of the clusters and the inter-cluster distance. Constructive interference phenomena were tuned through a systematic study of different geometrical configurations, thereby controlling confinement in quasi-bound states. Gaussian trap potentials have been used to simulate the imperfect barrier-well interface associated with disordered materials. Strongly localized states can be formed successfully despite weak disorder as illustrated by breaking the symmetry in the horizontal configuration. To this end, triangular cluster configurations were investigated under a variety of conditions including various shapes and orientations. The effects of disorder created effectively by the arbitary configurations destroy the Fano resonance, which is previlent in conductance spectra and consequently reduce the peak to valley ratio of the resonant peak in current vs. voltage curves. However the formation of two quasi-bound states is demonstrated, suggesting possible applications for disordered naturally grown systems of impurity clusters. This work addresses the controlled lifetime of quasi-bound states and can inform the design of fast switching devices based on high band gap materials by the astute incorporation of impurity clusters with specific geometrical configurations.
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