arXiv subjects

Natalya A. Zimbovskaya

Publications and source records attributed to Natalya A. Zimbovskaya.

At least 37 records · Page 2Linked to original sources

arXiv2013

Electric charge and potential distribution in twisted multilayer graphene

The specifics of charge screening and electrostatic potential spatial distribution in multilayered graphene films placed in between charged substrates is theoretically analyzed. It is shown that by varying the areal charge densities on the substrates and/or the thickness of the graphene stack one may tune the doped carriers distribution over the system. When the charge densities on the substrates are weak, the carriers distribution and electrostatic potential profile agree with semimetallic properties of graphene. However, when the amount of the donated charge is sufficiently large the transition to a metallic-like behavior of the graphene layers occurs. The possibilities for experimental observation of the predicted transition are discussed.

cond-mat.mes-hall↗

arXiv2013

Specific features of electric charge screening in few-layer graphene films

We present a non-linear Thomas-Fermi theory which describes the electric charge screening in the system including two charged substrate layers separated by a few-layered graphene film. We show that by increasing the charge at the interfaces, the system could be turned from the weak screening regime where the whole film responds to the external charge, to the strong screening regime where the external charge is screened by a surface charge distribution confined to the bounding graphene layers. The transition from weak to strong screening is shown to turn on relatively quickly, and it happens when the applied external charge/external field reaches a certain crossover magnitude. The possibilities for experimental observation of the predicted crossover are discussed.

cond-mat.mes-hall↗

arXiv2013

Electromagnetic quantum waves and their effect on the low temperature magnetoacoustic response of a quasi-two-dimensional metal

We theoretically analyze weakly attenuated electromagnetic waves in quasi-two-dimensional (Q2D) metals in high magnetic fields. Within the chosen geometry, the magnetic field is directed perpendicularly to the conducting layers of a Q2D conductor. We showed that longitudinal collective modes could propagate along the magnetic field provided that the Fermi surface is moderately corrugated. The considered waves speeds strongly depend on the magnetic field magnitude. Also, we analyzed interactions of these quantum waves with sound waves of fitting polarization and propagation direction, and we showed that such interaction may bring significant changes to the low temperature magnetoacoustic response of Q2D conductors.

cond-mat.mtrl-sci↗

arXiv2013

Inelastic electron transport through molecular junctions

Currently, molecular tunnel junctions are recognized as important active elements of various nanodevices. This gives a strong motivation to study physical mechanisms controlling electron transport through molecules. Electron motion through a molecular bridge is always somewhat affected by the environment, and the interactions with the invironment could change the energy of the traveling electron. Under certain conditions these inelastic effects may significantly modify electron transport characteristics. In the present work we describe inelastic and dissipative effects in the electron transport occurring due to the molecular bridge vibrations and stochastic thermally activated ion motions. We intentionally use simple models and computational techniques to keep a reader focused on the physics of inelastic electron transport in molecular tunnel junctions. We consider electron-vibron interactions and their manifestations in the inelastic tunneling spectra, polaronic effects and dissipative electron transport. Also, we briefly discuss long-range electron transfer reactions in macromolecules and their relation to the electron transport through molecular junctions.

cond-mat.mes-hall↗

arXiv2013

On the electron transport in conducting polymer nanofibers

Recent advances in synthesis and electrical characterization of nanofibers and nanotubes made out of various conjugated polymers attract attention of the research community to studies of transport properties of these materials. In this work we present a theoretical analysis of electron transport in polymer nanofibers assuming them to be in conducting state. We treat a conducting polymer as a network of metallic-like grains embedded in poorly conducting environment, which consists of randomly distributed polymeric chains. We analyze the contribution from intergrain electron resonance tunneling via intermediate states localized on the polymeric chains between the grains. Correspondingly, we apply the quantum theory of conduction in mesoscopic systems to analyze this transport mechanism. We show that the contribution of resonance electron tunneling to the intergrain electron transport may be predominating, as follows from experiments on the electrical characterization of single polyaniline nanofibers. We study the effect of temperature on the transport characteristics. We represent the thermal environment as a phonon bath coupled to the intermediate state, which provides electron tunneling between the metallic-like grains. Using the Buttiker model within the scattering matrix formalism combined with the nonequilibrium Green's functions technique, we show that temperature dependencies of both current and conductance associated with the intergrain electron tunneling, differ from those typical for other conduction mechanisms in conducting polymers. Also, we demonstrate that under certain conditions the phonon bath may cause suppression of the original intermediate state accompanied by emergence of new states for electron tunneling. The temperature dependencies of the magnitudes of the peaks in the transmission corresponding to these new states are analyzed.

cond-mat.mes-hall↗

arXiv2010

Electron transport through asymmetric ferroelectric tunnel junctions: current-voltage characteristics

We have carried out calculations of current-voltage characteristics for the electron tunnel current through a junction with a thin insulating ferroelectric barrier assuming that interface transmissions for the left and right interfaces noticeably differ due to dissimilarity of the interfaces. Obtained conductance versus voltage and current versus voltage curves exhibit well distinguishable asymmetric hysteresis. We show that the asymmetry in the hysteretic effects could originate from the asymmetric bias voltage profile inside the junction. In particular, we analyze the hysteresis asymmetries occurring when the bias voltage distribution is low sensitive to the spontaneous polarization reversal.

cond-mat.mtrl-sci↗

arXiv2009

Quantum oscillations in the high frequency magnetoacoustic response of a quasi-two-dimensional metal

In this work we present the results of theoretical analysis of magnetic quantum oscillations of the velocity and attenuation of high frequency ultrasound waves traveling in quasi-two-dimensional conductors. We chose a geometry where the wave vector of the longitudinal sound wave and the external magnetic field are directed along the axis of symmetry of the Fermi surface. Assuming a moderately weak Fermi surface corrugation we showed that the oscillating correction to the sound velocity may include a special term besides an ordinary contribution originating from quantum oscillations of the charge carriers density of states at the Fermi surface. This additional term is generated by a "phase stability" resonance occurring when the charge carriers velocity in the direction of the wave propagation equals the sound velocity. The two oscillating contributions to the sound velocity are shown to differ in phase and shape, and they may have the same order of magnitude. The appearance of the extra term may bring significant changes in magnetic quantum oscillations of the velocity of sound in Q2D conductors, especially at low temperatures.

cond-mat.mtrl-sci↗

arXiv2009

Vibration-induced inelastic effects in the electron transport through multisite molecular bridges

We theoretically analyzed inelastic effects in the electron transport through molecular junctions originating from electron-vibron interactions. The molecular bridge was simulated by a periodic chain of identical interacting hydrogen-like atoms providing a set of energy states for the electron tunneling. To avoid difficulties inevitably arising when advanced computational techniques are employed to study inelastic electron transport through multilevel bridges, we propose and develop a semiphenomenological approach. The latter is based on the Buttiker's dephasing model within the scattering matrix formalism. The advantage of the proposed approach is that it allows to analytically study various inelastic effects on the conduction through molecular junctions including multilevel bridges. Here, we apply this approach to describe features associated with electron energy transfer to vibrational phonons which appear in the inelastic tunneling spectra of electrons. In the particular case of a single level bridge our results agree with those obtained by self-consitent calculations carried out within the nonequilibrium Green's functions method validating the usefulness of the suggested approach.

cond-mat.mtrl-sci↗

arXiv2009

Nanoparticle networks as chemoselective sensing devices

We theoretically analyzed transport properties of a molecular network constructed of gold nanoparticles linked with oligophenylenevinulene (OPV) molecules. We showed that the conductance of such system was strongly reduced when trinitrotoluene (TNT) became attached to the OPV linkers in the network. The reported results are based on the ab inicio electronic structure calculations. These results corroborate and elucidate experiments which revealed significant drops in the conductance the network while the latter was exposed to TNT vapors. The results suggest that the detected sensitivity of transport characteristics of the considered nanoparticle network to TNT may be used to design a sensing nanodevice.

cond-mat.mtrl-sci↗

arXiv2008

Effect of Fermi-liquid interactions on the low-temperature de Haas - van Alphen oscillations in quasi-two-dimensional conductors

In this work we present the results of theoretical analysis of the de Haas-van Alphen oscillations in quasi-two-dimensional conductors. We have been studying the effect of the Fermi-liquid correlations of charge carriers on the above oscillations. It was shown that at reasonably low temperatures and weak electron scattering the Fermi-liquid interactions may cause noticeable changes in both amplitude and shape of the oscillations even at realistically small values of the Fermi-liquid parameters. Also, we show that the Fermi-liquid interactions in the system of the charge carriers may cause magnetic instability of a quasi-two-dimensional conductor near the peaks of quantum oscillations in the electron density of states at the Fermi surface, indicating the possibility for the diamagnetic phase transition within the relevant ranges of the applied magnetic fields.

cond-mat.mtrl-sci↗

arXiv2008

The electron transport through a quantum dot in the Coulomb blockade regime: Non-equilibrium Green's functions based model

We explore electron transport through a quantum dot coupled to the source and drain charge reservoirs We trace the transition from the Coulomb blockade regime to Kondo regime in the electron transport through the dot occuring when we gradually strengthen the coupling of the dot to the charge reservoirs. The current-voltage $(I-V)$ characteristics are calculated using the equations of motion approach within the nonequilibrium Green's functions formalism (NEGF) beyond the Hartree-Fock approximation. We show that within the Coulomb blockade regime the $I-V$ characteristics for the quantum dot containing a single spin-degenerated level with the energy $E_0 $ include two steps whose locations are determined by the values of $ E_0 $ and the energy of Coulomb interaction of electrons in the dot $U.$ The heights of the steps are related as $2:1$ which is consistent with the results obtained by means of the transition rate equations.

cond-mat.str-el↗

arXiv2008

Inelastic electron transport in polymer nanofibers

In this paper we present theoretical analysis of the electron transport in conducting polymers. We concentrate on the study of the effects of temperature on characteristics of the transport. We treat a conducting polymers in a metal state as a network of metallic-like grains connected by electron quantum tunneling via intermediate state localized on a polymer chain between the grains. To analyze the effects of temperature on this kind of electron intergrain transport we represent the thermal environment as a phonon bath coupled to the intermediate state. The electron transmission is computed using the Buttiker model within the scattering matrix formalism. This approach is further developed, and the dephasing parameter is expessed in terms of relevant energies including the thermal energy. It is shown that temperature dependencies of both current and conductance associated with the above transport mechanism differ from those typical for other conduction mechanisms in conducting polymers. This could be useful to separate out the contribution from the intergrain electron tunneling to the net electric current in transport experiments on various polymer nanofibers. The proposed model could be used to analyze inelastic electron transport through molecular junctions.

cond-mat.mtrl-sci↗

arXiv2008

Negative differential resistance in molecular junctions: The effect of the electrodes electronic structure

We have carried out calculations of electron transport through a metal-molecule-metal junction with metal nanoclusters taking the part of electrodes. We show that negative differential resistance peaks could appear in the current-voltage curves. The peaks arise due to narrow features in the electron density of states of the metal clusters. The proposed analysis is based on the ab initio computations of the relevant wave functions and energies within the framework of the density functional theory using NRLMOL software package.

cond-mat.mtrl-sci↗

arXiv2008

On the low frequency electromagnetic waves in quasi-two-dimensional metals

Here, we theoretically analyze spectra of weakly attenuated electromagnetic waves which may appear in a Fermi-liquid of charge carriers in quasi-two-dimensional (Q2D) layered conductors when an external magnetic field is applied perpendicularly to the conducting layers. We study transverse modes propagating along the magnetic field. The frequencies of the modes are assumed to be lower than the cyclotron frequency of the charge carriers. It is shown that Fermi-liquid interaction of the charge carriers in Q2D conductors gives rise to a mode which cannot appear in a gase of charged quasiparticles, as well as it happens in conventional metals. Also, we show that the Fermi surface plofile may cause significant changes in the waves spectra and we analyze these changes.

cond-mat.mtrl-sci↗

arXiv2007

Fermi-liquid and Fermi surface geometry effects in propagation of low frequency electromagnetic waves through thin metal films

In the present work we theoretically analyze the contribution from a transverse Fermi-liquid collective mode to the transmission of electromagnetic waves through a thin film of a clean metal in the presence of a strong external magnetic field. We show that at the appropriate Fermi surface geometry the transverse Fermi-liquid wave may appear in conduction electrons liquid at frequencies $ω$ significantly smaller than the cyclotron frequency of charge carriers $Ω$ provided that the mean collision frequency $τ^{-1}$ is smaller than $ω.$ Also, we show that in realistic metals size oscillations in the transmission coefficient associated with the Firmi-liquid mode may be observable in experiments. Under certain conditions these oscillations may predominate over the remaining size effects in the transmission coefficient.

cond-mat.mtrl-sci↗

arXiv2007

On the dissipative effects in the electron transport through conducting polymer nanofibers

Here, we study the effects of stochastic nuclear motions on the electron transport in doped polymer fibers assuming the conducting state of the material. We treat conducting polymers as granular metals and apply the quantum theory of conduction in mesoscopic systems to describe the electron transport between the metalliclike granules. To analyze the effects of nuclear motions we mimic them by the phonon bath, and we include the electron-phonon interactions in consideration. Our results show that the phonon bath plays a crucial part in the intergrain electron transport at moderately low and room temperatures suppressing the original intermediate state for the resonance electron tunneling, and producing new states which support the electron transport.

cond-mat.soft↗

arXiv2007

Fermi-liquid effects in the transresistivity in quantum Hall double layers near $ν= 1/2 $

Here, we present theoretical studies of the temperature and magnetic field dependences of the Coulomb drag transresistivity between two parallel layers of two dimensional electron gases in quantum Hall regime near half filling of the lowest Landau level. It is shown that Fermi-liquid interactions between the relevant quasiparticles could give a significant effect on the transresistivity, providing its independence of the interlayer spacing for spacings taking on values reported in the experiments. Obtained results agree with the experimental evidence.

cond-mat.mes-hall↗

arXiv2007

On the de Haas - van Alphen oscillations in quasi-two-dimensional metals: effect of the Fermi surface curvature

Here, we present the results of theoretical analysis of the de Haas-van Alphen oscillations in quasi-two-dimensional normal metals. We had been studying effects of the Fermi surface (FS) shape on these oscillations. It was shown that the effects could be revealed and well pronounced when the FS curvature becomes zero at cross-sections with extremal cross-sectional areas. In this case both shape and amplitude of the oscillations could be significantly changed. Also, we analyze the effect of the FS local geometry on the angular dependencies of the oscillation amplitudes when the magnetic field is tilted away from the FS symmetry axis by the angle $θ.$ We show that a peak appears at $θ\approx 0$ whose height could be of the same order as the maximum at the Yamaji angle. This peak emerges when the FS includes zero curvature cross-sections of extremal areas. Such maximum was observed in experiments on the $α-(BETS)_4TIHg(SeCN)_4.$ The obtained results could be applied to organic metals and other quasi-two-dimensional compounds.

cond-mat.mtrl-sci↗