arXiv subjects

E. G. Mishchenko

Publications and source records attributed to E. G. Mishchenko.

At least 55 records · Page 3Linked to original sources

arXiv2007

Effect of electron-electron interactions on the conductivity of clean graphene

Minimal conductivity of a single undoped graphene layer is known to be of the order of the conductance quantum, independent of the electron velocity. We show that this universality does not survive electron-electron interaction which results in the non-trivial frequency dependence. We begin with analyzing the perturbation theory in the interaction parameter 'g' for the electron self-energy and observe the failure of the random-phase approximation. The optical conductivity is then derived from the quantum kinetic equation and the exact result is obtained in the limit when g << 1 << g lnω.

cond-mat.mes-hall↗

arXiv2006

Planar array of semiconducting nanotubes in external electric field: Collective screening and polarizability

We study theoretically the charge separation in a planar array of semiconducting nanotubes (NTs) of length, 2h, placed in external electric field, F, parallel to their axes. By employing the conformal mapping, we find analytically the exact distribution of the induced charge density for arbitrary ratio of the gap, E_g, and the voltage drop, eFh, across the NT. We use the result obtained to (i) trace the narrowing of the neutral strip at center of the NT with increasing F; (ii) analyze the polarizability of the array as a function of E_g; (iii) study the field enhancement near the tips.

cond-mat.mes-hall↗

arXiv2006

Generation of spin current by Coulomb drag

Coulomb drag between two quantum wires is exponentially sensitive to the mismatch of their electronic densities. The application of a magnetic field can compensate this mismatch for electrons of opposite spin directions in different wires. The resulting enhanced momentum transfer leads to the conversion of the charge current in the active wire to the spin current in the passive wire.

cond-mat.mes-hall↗

arXiv2006

Tunneling between 2D electron layers with correlated disorder: anomalous sensitivity to spin-orbit coupling

Tunneling between two-dimensional electron layers with mutually correlated disorder potentials is studied theoretically. Due to this correlation, the diffusive eigenstates in different layers are almost orthogonal to each other. As a result, a peak in the tunnel I-V characteristics shifts towards small bias, V. This "protects" the peak against the interaction-induced smearing, since the relaxation rate near the Fermi level is low. If the correlation in disorder potentials is complete, the peak position and width are governed by the spin-orbit coupling in the layers; this coupling lifts the orthogonality of the eigenstates. Possibility to use inter-layer tunneling for experimental determination of weak intrinsic spin-orbit splitting of the Fermi surface is discussed.

cond-mat.mes-hall↗

arXiv2006

Polarized Electric Current in Semiclassical Transport with Spin-Orbit Interaction

Semiclassical solutions of two-dimensional Schrodinger equation with spin-orbit interaction and smooth potential are considered. In the leading order, spin polarization is in-plane and follows the evolution of the electron momentum for a given subband. Out-of-plane spin polarization appears as a quantum correction, for which an explicit expression is obtained. We demonstrate how spin-polarized currents can be achieved with the help of a barrier or quantum point contact open for transmission only in the lower subband.

cond-mat.mes-hall↗

arXiv2006

Electrostatics of straight and bent nanotubes

Response of a single-walled carbon nanotube to external electric field, F, is calculated analytically within the classical electrostatics. Field-induced charge density distribution is approximately linear along the axis of metallic nanotube and depends rather weakly, as ln(h/r), on the nanotube length, h, (here r is the nanotube radius). In a semiconducting nanotube with a gap, E_g, charge separation occurs as F exceeds the threshold value F_{th}=E_g/eh. For F>F_{th}, positively and negatively charged regions at the ends of nanotube are separated by a neutral strip in the middle. For bent nanotubes the number of neutral strips can be one or two depending on the direction of F.

cond-mat.mes-hall↗

arXiv2006

Penetration of external field into regular and random arrays of nanotubes: Implications for field emission

We develop an analytical theory of polarization of a vertically aligned array of carbon nanotubes (NTs) in external electric field. Such arrays are commonly utilized in field-emission devices, due to the known electrostatic effect of strong field enhancement near the tip of an individual NT. A small ratio of the NT radius to the separation between neighboring NTs allows us to obtain asymptotically exact solution for the distribution of induced charge density along the NT axes. For a regular array, this solution allows us to trace the suppression of the field penetration with increasing the density of NTs in the array. We demonstrate that for a random array, fluctuations in the NT density terminate the applicability of our result at distances from the NT tips much larger than the field penetration depth, where the induced charge density is already exponentially small. Our prime conclusion is that, due to collective screening of the external field by the array, the field-emission current decreases drastically for dense arrays compared to an individual NT. We argue that the reason why the strong field emission, described by the Fowler-Nordheim law and observed in realistic arrays, is the strong dispersion in heights of the constituting NTs.

cond-mat.mes-hall↗

arXiv2005

Small-angle impurity scattering and the spin Hall conductivity in 2D systems

An arbitrarily small concentration of impurities can affect the spin Hall conductivity in a two-dimensional semiconductor system. We develop a Boltzmann-like equation that can be used for impurity scattering with arbitrary angular dependence, and for arbitrary angular dependence of the spin-orbit field b(k) around the Fermi surface. For a model applicable to a 2D hole system in GaAs, if the impurity scattering is not isotropic, we find that the spin Hall conductivity depends on the derivative of b with respect to the energy and on deviations from a parabolic band structure, as well as on the angular dependence of the scattering. In principle, the resulting spin Hall conductivity can be larger or smaller than the ``intrinsic value'', and can have opposite sign. In the limit of small angle scattering, in a model appropriate for small hole concentrations, where the band is parabolic and b ~ k^3, the spin Hall conductivity has opposite sign from the intrinsic value, and has larger magnitude. Our analysis assumes that the spin-orbit splitting $b$ and the transport scattering rate tau^{-1} are both small compared to the Fermi energy, but the method is valid for for arbitrary value of b*tau.

cond-mat.mes-hall↗

arXiv2005

Infrared absorption and Raman scattering on coupled plasmon--phonon modes in superlattices

We consider theoretically a superlattice formed by thin conducting layers separated spatially between insulating layers. The dispersion of two coupled phonon-plasmon modes of the system is analyzed by using Maxwell's equations, with the influence of retardation included. Both transmission for the finite plate as well as absorption for the semi-infinite superlattice in the infrared are calculated. Reflectance minima are determined by the longitudinal and transverse phonon frequencies in the insulating layers and by the density-state singularities of the coupled modes. We evaluate also the Raman cross section from the semi-infinite superlattice.

cond-mat.mtrl-sci↗

arXiv2005

Pseudospin ferromagnetism in double-quantum-wire systems

We propose that a pseudospin ferromagnetic (i.e inter-wire coherent) state can exist in a system of two parallel wires of finite width in the presence of a perpendicular magnetic field. This novel quantum many-body state appears when the inter wire distance decreases below a certain critical value which depends on the magnetic field. We determine the phase boundary of the ferromagnetic phase by analyzing the softening of the spin-mode velocity using the bosonization approach. We also discuss signatures of this state in tunneling and Coulomb drag experiments.

cond-mat.str-el↗

arXiv2005

Breached Superfluidity via P-Wave Coupling

Anisotropic pairing between fermion species with different fermi momenta opens two-dimensional areas of gapless excitations, thus producing a spatially homogeneous state with coexisting superfluid and normal fluids. This breached pairing state is stable and robust for arbitrarily small mismatch and weak p-wave coupling.

cond-mat.supr-con↗

arXiv2004

Spin current and polarization in impure 2D electron systems with spin-orbit coupling

We derive the transport equations for two-dimensional electron systems with spin-orbit interaction and short-range spin-independent disorder. In the limit of slow spatial variations of the electron distribution we obtain coupled diffusion equations for the electron density and spin. Using these equations we calculate electric-field induced spin accumulation in a finite-size sample for arbitrary ratio between spin-orbit energy splitting and elastic scattering rate. We demonstrate that the spin-Hall conductivity vanishes in an infinite system independent of this ratio.

cond-mat.mes-hall↗

arXiv2004

Plasmon attenuation and optical conductivity of a two-dimensional electron gas

In a ballistic two-dimensional electron gas, the Landau damping does not lead to plasmon attenuation in a broad interval of wave vectors q << k_F. Similarly, it does not contribute to the optical conductivity σ(ω, q) in a wide domain of its arguments, E_F > ω> qv_F, where E_F, k_F and v_F are, respectively, the Fermi energy, wavevector and velocity of the electrons. We identify processes that result in the plasmon attenuation in the absence of Landau damping. These processes are: the excitation of two electron-hole pairs, phonon-assisted excitation of one pair, and a direct plasmon-phonon conversion. We evaluate the corresponding contributions to the plasmon linewidth and to the optical conductivity.

cond-mat.mes-hall↗

arXiv2004

Fluctuations of radiation from a chaotic laser below threshold

Radiation from a chaotic cavity filled with gain medium is considered. A set of coupled equations describing the photon density and the population of gain medium is proposed and solved. The spectral distribution and fluctuations of the radiation are found. The full noise is a result of a competition between positive correlations of photons with equal frequencies (due to stimulated emission and chaotic scattering) which increase fluctuations, and a suppression due to interaction with a gain medium which leads to negative correlations between photons. The latter effect is responsible for a pronounced suppression of the photonic noise as compared to the linear theory predictions.

cond-mat.mes-hall↗

arXiv2003

Coulomb drag by small momentum transfer between quantum wires

We demonstrate that in a wide range of temperatures Coulomb drag between two weakly coupled quantum wires is dominated by processes with a small interwire momentum transfer. Such processes, not accounted for in the conventional Luttinger liquid theory, cause drag only because the electron dispersion relation is not linear. The corresponding contribution to the drag resistance scales with temperature as T^2 if the wires are identical, and as T^5 if the wires are different.

cond-mat.mes-hall↗

arXiv2003

Transport equations for a two-dimensional electron gas with spin-orbit interaction

The transport equations for a two-dimensional electron gas with spin-orbit interaction are presented. The distribution function is a 2x2-matrix in the spin space. Particle and energy conservation laws determine the expressions for the electric current and the energy flow. The derived transport equations are applied to the spin-splitting of a wave packed and to the calculation of the structure factor and the dynamic conductivity.

cond-mat.mes-hall↗

arXiv2003

Shot noise in a diffusive F-N-F spin valve

Fluctuations of electric current in a spin valve consisting of a diffusive conductor connected to ferromagnetic leads and operated in the giant magnetoresistance regime are studied. It is shown that a new source of fluctuations due to spin-flip scattering enhances strongly shot noise up to a point where the Fano factor approaches the full Poissonian value.

cond-mat.mes-hall↗

arXiv2003

Thermal conductivity of a two-dimensional electron gas with Coulomb interaction

We demonstrate that forward electron-electron scattering due to Coulomb interation in a two-dimensional ballistic electron gas leads to the (T\ln {T})^{-1} temperature dependence of the thermal conductivity, which is logarithmically suppressed compared to the usual Fermi liquid behaviour.

cond-mat.mes-hall↗