Heat conduction in 2D strongly-coupled dusty plasmas

We perform non-equilibrium simulations to study heat conduction in two-dimensional strongly coupled dusty plasmas. Temperature gradients are established by heating one part of the otherwise equilibrium system to a higher temperature. Heat conductivity is measured directly from the stationary temperature profile and heat flux. Particular attention is paid to the influence of damping effect on the heat conduction. It is found that the heat conductivity increases with the decrease of the damping rate, while its magnitude agrees with previous experimental measurement.Comment: 4 pages, 2 figures, presented in SCCS2008 conferenc

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.

Donut and dynamic polarization effects in proton channeling through carbon nanotubes

We investigate the angular and spatial distributions of protons of the energy of 0.223 MeV after channeling through an (11,~9) single-wall carbon nanotube of the length of 0.2 $\mu$m. The proton incident angle is varied between 0 and 10 mrad, being close to the critical angle for channeling. We show that, as the proton incident angle increases and approaches the critical angle for channeling, a ring-like structure is developed in the angular distribution - donut effect. We demonstrate that it is the rainbow effect. When the proton incident angle is between zero and a half of the critical angle for channeling, the image force affects considerably the number and positions of the maxima of the angular and spatial distributions. However, when the proton incident angle is close to the critical angle for channeling, its influence on the angular and spatial distributions is reduced strongly. We demonstrate that the increase of the proton incident angle can lead to a significant rearrangement of the propagating protons within the nanotube. This effect may be used to locate atomic impurities in nanotubes as well as for creating nanosized proton beams to be used in materials science, biology and medicine.Comment: 17 pages, 14 figure

Wave spectra of 2D dusty plasma solids and liquids

Brownian dynamics simulations were carried out to study wave spectra of two-dimensional dusty plasma liquids and solids for a wide range of wavelengths. The existence of a longitudinal dust thermal mode was confirmed in simulations, and a cutoff wavenumber in the transverse mode was measured. Dispersion relations, resulting from simulations, were compared with those from analytical theories, such as the random-phase approximation (RPA), quasi-localized charged approximation (QLCA), and harmonic approximation (HA). An overall good agreement between the QLCA and simulations was found for wide ranges of states and wavelengths after taking into account the direct thermal effect in the QLCA, while for the RPA and HA good agreement with simulations were found in the high and low temperature limits, respectively.Comment: 26 pages, 9 figure

Friction force on slow charges moving over supported graphene

We provide a theoretical model that describes the dielectric coupling of a 2D layer of graphene, represented by a polarization function in the Random Phase Approximation, and a semi-infinite 3D substrate, represented by a surface response function in a non-local formulation. We concentrate on the role of the dynamic response of the substrate for low-frequency excitations of the combined graphene-substrate system, which give rise to the stopping force on slowly moving charges above graphene. A comparison of the dielectric loss function with experimental HREELS data for graphene on a SiC substrate is used to estimate the damping rate in graphene and to reveal the importance of phonon excitations in an insulating substrate. A signature of the hybridization between graphene's pi plasmon and the substrate's phonon is found in the stopping force. A friction coefficient that is calculated for slow charges moving above graphene on a metallic substrate shows an interplay between the low-energy single-particle excitations in both systems.Comment: 13 pages, 5 figures, submitted to Nanotechnology for a special issue related to the NGC 2009 conference (http://asdn.net/ngc2009/index.shtml

The effects of dielectric decrement and finite ion size on differential capacitance of electrolytically gated graphene

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.cplett.2018.04.030 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/We analyze the effects of dielectric decrement and finite ion size in an aqueous electrolyte on the capacitance of a graphene electrode, and make comparisons with the effects of dielectric saturation combined with finite ion size. We first derive conditions for the cross-over from a camel-shaped to a bell-shaped capacitance of the diffuse layer. We show next that the total capacitance is dominated by a V-shaped quantum capacitance of graphene at low potentials. A broad peak develops in the total capacitance at high potentials, which is sensitive to the ion size with dielectric saturation, but is stable with dielectric decrement.Natural Sciences and Engineering Research Council of Canada (ZLM: Grant No. 2016-03689

Wave spectra of 2D Yukawa solids and liquids in the presence of a magnetic field

Thermally excited phonon spectra of 2D Yukawa solids and liquids in the presence of an external magnetic field are studied using computer simulations. Special attention is paid to the variation of wave spectra in terms of several key parameters, such as the strength of coupling, the screening parameter, and the intensity of the magnetic field. In addition, comparisons are made with several analytical theories, including random-phase approximation, quasi-localized charge approximation, and harmonic approximation, and the validity of those theories is discussed in the present context.Comment: 21 pages 11 figure