Dynamic polarization of graphene by moving external charges: random phase approximation

We evaluate the stopping and image forces on a charged particle moving parallel to a doped sheet of graphene by using the dielectric response formalism for graphene's $\pi$-electron bands in the random phase approximation (RPA). The forces are presented as functions of the particle speed and the particle distance for a broad range of charge-carrier densities in graphene. A detailed comparison with the results from a kinetic equation model reveal the importance of inter-band single-particle excitations in the RPA model for high particle speeds. We also consider the effects of a finite gap between graphene and a supporting substrate, as well as the effects of a finite damping rate that is included through the use of Mermin's procedure. The damping rate is estimated from a tentative comparison of the Mermin loss function with a HREELS experiment. In the limit of low particle speeds, several analytical results are obtained for the friction coefficient that show an intricate relationship between the charge-carrier density, the damping rate, and the particle distance, which may be relevant to surface processes and electrochemistry involving graphene.Comment: 14 pages, 10 figures, accepted for publication in Phys. Rev.

Time Delay in Thin Dielectric Slabs with Saturable Nonlinearity

Time delays for an intense transverse electric wave propagating through a slab with saturable nonlinearity are investigated. The nonlinearity is assumed in a form of the Vinetskii-Kukhtarev model, which is relevant for the slabs made of nonlinear photorefractive crystals, such as GaAs and LiNbO(3), which feature a saturable nonlinearity. The expressions for the group delay and the dwell time are derived and the relation between them is studied. It is shown that the difference between them has three different contributions. The first one corresponds to the self-interference associated with the dispersion of the medium surrounding the slab. The other two appear due to the nonlinearity of the slab and oblique incidence of the transverse electric wave. All the results are compared with the case of dielectric slabs with cubic (Kerr) nonlinearity.10th Annual Conference of the Materials-Research-Society-of-Serbia, Sep 08-12, 2008, Herceg Novi, Montenegr

Refractive properties of metamaterial composed of InGaAs layers with alternating doping densities

The aspects of light propagation through a semiconductor metamaterial (SMM) which consists of two alternating differently doped In0.53Ga0.47As layers are studied analytically and numerically. A general analytical expression for the effective index of refraction of the Poynting vector is derived for periodic structure composed of two alternating layers of absorptive and dispersive semiconductors and light propagation is simulated by finite-difference-time-domain method. Negative values of the effective refractive index with low absorption are observed in the mid-infrared frequency range. The main advantage of this design is the possibility to control the frequency region with negative effective refractive index by changing the doping densities of the layers

Goos-Hanchen shift and time delay in dispersive nonlinear media

We present an analysis of the influence of the Goos-Hanchen effect on tunneling times, group delay and dwell time, of electromagnetic waves propagating through an obstacle made of left-handed metamaterial embedded in a dielectric which exhibits saturable type of nonlinearity. The derived equations show that only the group delay, is affected by the Goos-Hanchen shift without any impact on the dwell time. Besides the reduction of the group delay, the most remarkable result is the possibility for total reduction of the Goos-Hanchen shift for finite incident angles. These phenomena are observable in the frequency region for which metamaterial exhibits negative index of refraction. (C) 2011 Elsevier B.V. All rights reserved

Influence of the Goos-Hanchen Shift on Tunneling Times in Dispersive Nonlinear Media

The Goos-Minchen effect is an optical phenomenon defined as a displacement of the reflected beam of linearly polarized light after the total internal reflection, which occurs perpendicularly to the direction of propagation. Due to this effect, when an optical wave propagates through a barrier, tunneling times may change accordingly. In this paper, we consider the impact of the Goos-Hanchen effect on group delay and dwell time for electromagnetic wave propagating through a nonlinear dispersive slab placed inside linear dispersive surroundings. Numerical calculations are performed for the special case, namely a double negative index metamaterial embedded into a material with a saturable nonlinearity, when a background medium is vacuum. The numerical results for tunneling times are calculated when the Goos-Hanchen effect is observed. It is shown that this approach gives more accurate expressions for tunneling times when the angle of incidence has a non-zero value.International School and Conference on Photonics (PHOTONICA09), Aug 24-28, 2009, Belgrade, Serbi