E. G. Mishchenko

Spin Current and Polarization in Impure Two-Dimensional Electron Systems with Spin-Orbit Coupling

We derive the transport equations for two-dimensional electron systems with Rashba spin-orbit interaction and short-range spin-independent disorder. In the limit of slow spatial variations, we obtain coupled diffusion equations for the electron density and spin. Using these equations we calculate electric-field induced spin accumulation and spin current in a finite-size sample for an arbitrary ratio between spin-orbit energy splitting Delta and elastic scattering rate tau(-1). We demonstrate that the spin-Hall conductivity vanishes in an infinite system independent of this ratio.

Guided plasmons in graphene p-n junctions.

Spatial separation of electrons and holes in graphene gives rise to the existence of plasmon waves confined to the boundary region. A theory of such guided plasmon modes within hydrodynamics of electron-hole liquid is developed. For plasmon wavelengths smaller than the size of charged domains, plasmon dispersion is found to be omega proportional to q(1/4). The frequency, velocity, and direction of propagation of guided plasmon modes can be easily controlled by the external electric field. In the presence of a magnetic field, a spectrum of additional gapless magnetoplasmon excitations is obtained. Our findings indicate that graphene is a promising material for nanoplasmonics.

Electron-lattice kinetics of metals heated by ultrashort laser pulses

We propose a kinetic model of transient nonequilibrium phenomena in metals exposed to ultrashort laser pulses when heated electrons affect the lattice through direct electron-phonon interaction. This model describes the destruction of a metal under intense laser pumping. We derive the system of equations for the metal, which consists of hot electrons and a cold lattice. Hot electrons are described with the help of the Boltzmann equation and equation of thermoconductivity. We use the equations of motion for lattice displacements with the electron force included. The lattice deformation is estimated immediately after the laser pulse up to the time of electron temperature relaxation. An estimate shows that the ablation regime can be achieved.

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 2\ifmmode\times\else\texttimes\fi{}2-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 packet and to the calculation of the structure factor and the dynamic conductivity.

Dynamic Conductivity in Graphene beyond Linear Response

The independence of the dynamic conductivity of intrinsic graphene of frequency takes its origin in the compensation of the vanishing density of states by the diverging matrix element of the corresponding interband transition. The applicability of the linear response approach, however, breaks down when this matrix element becomes comparable with the inverse electron lifetime. We show that the physics of the ac conductivity in this regime is determined by Rabi oscillations and obtain it beyond the first-order perturbation theory. Under strong applied electric fields, the induced current eventually saturates at a value determined by the frequency and the lifetime. We also calculate the electromagnetic response of a graphene sheet and find that the optical transparency is increased by the nonlinear effects and make experimental predictions.

Zero-bias anomaly in disordered wires.

We calculate the low-energy tunneling density of states nu(epsilon,T) of an N-channel disordered wire, taking into account the electron-electron interaction nonperturbatively. The finite scattering rate 1/tau results in a crossover from the Luttinger liquid behavior at higher energies, nu proportional to epsilon(alpha), to the exponential dependence nu(epsilon,T = 0) proportional to exp(-epsilon*/epsilon) at low energies, where epsilon* proportional to 1/(Ntau). At finite temperature T, the tunneling density of states depends on the energy through the dimensionless variable epsilon/root square[epsilon*T]. At the Fermi level nu(epsilon = 0,T)proportional to exp(-root square[epsilon*/T]).

Two electrons in a quantum dot: a semiclassical approach

The spectra of two electrons in a parabolic quantum dot in a magnetic field are obtained using the WKB approximation. No restrictions are imposed on the value of the electron-electron interaction. A simple approximation allowing an exact solution to be obtained for the interaction between two electrons in a quantum dot is proposed. It reproduces all of the qualitative features of the two-electron spectrum. Quantitatively, it is in good agreement with the WKB solution for the range of parameters of experimental interest.

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 T2 if the wires are identical, and as T5 if the wires are different.

Spin hall edge spin polarization in a ballistic 2D electron system.

Universal properties of the spin Hall effect in ballistic 2D electron systems are addressed. The net spin polarization across the edge of the conductor is second order, approximately lambda2, in spin-orbit coupling constant independent of the form of the boundary potential, with the contributions of normal and evanescent modes each being approximately radical lambda but of opposite signs. This general result is confirmed by the analytical solution for a hard-wall boundary, which also yields the detailed distribution of the local spin polarization. The latter shows fast (Friedel) oscillations with the spin-orbit coupling entering via the period of slow beatings only. Long-wavelength contributions of evanescent and normal modes exactly cancel each other in the spectral distribution of the local spin density.

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.