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We have investigated the role of pseudospin polarization in electron wave packet dynamics in pristine graphene and in a graphene antidot lattice subject to an external magnetic field. Employing a Green's function formalism, we show that the electron dynamics can be controlled by tuning pseudospin polarization. We find that in Landau quantized pristine graphene both the propagation of an electron wave packet and Zitterbewegung oscillations strongly depend on pseudospin polarization. The electron wave packet is found to propagate in the direction of initial pseudospin polarization. We also show that, in this system, the propagation of an electron can be enhanced in any desired direction by carving a one dimensional antidot lattice in that direction. The study suggests that a graphene antidot lattice can serve as a channel for electron transport with the possibility of tunability by means of pseudospin polarization, antidot potential and applied normal magnetic field strength., This is the version 2 of the article which has been accepted by Journal of Applied Physics for publication. It contains 12 pages and 6 figures

We analyze the electrodynamic interaction of an incident terahertz electromagnetic wave with a current-carrying lateral double-quantum-wire superlattice (at normal incidence). The superlattice (in the x-y plane) is taken to consist of two parallel quantum-wire sublattices, each of period d, shifted with respect to each other by distance Δ in the transverse y direction. The parallel quantum wires of the sublattices are all oriented in the x direction. The two sublattices are taken to carry equal steady currents in opposite directions, and are coupled by Coulomb forces alone, with tunneling neglected. We recently showed that quasi-one-dimensional plasmons of such double-quantum-wire superlattice systems become unstable when the electron drift velocity falls between the phase velocities of the acoustic and optical plasmon modes of the Coulomb-coupled wire subsystems. Here, we employ a random phase approximation for plasmon dispersion taken jointly with the full system of Maxwell equations to describe the ele...

We analyze electron transport through a biased asymmetric double-dot system in a parallel arrangement between leads. We show that the imposition of a dot-to-dot bias induces changes in the symmetry of the wave functions associated with the double-dot energy levels, resulting in a dip in the dependence of the lead-to-lead current on dot-to-dot bias. We also demonstrate that when the dot-to-dot bias compensates (energetically) the structure asymmetry, the lead-to-lead current will be an oscillating function of an applied magnetic field in the case in which only one of the double-dot levels is conductive. However, destructive interference between different parts of the same dot gives rise to suppression of current at high magnetic fields.

The terahertz absorption spectrum of plasmon modes in a grid-gated double-quantum-well (DQW) field-effect transistor structure is analyzed theoretically and numerically using a first principles electromagnetic approach and is shown to faithfully reproduce important physical features of recent experimental observations. We find that the essential character of the response—multiple resonances corresponding to spatial harmonics of standing plasmons under the metal grating—is caused by the static spatial modulation of electron density in the channel. Higher order plasmon modes become more optically active as the depth of the electron density modulation in the DQW tends towards unity. The maximum absorbance, at plasma resonance, is shown to be 1/2. Furthermore, the strongest absorption also occurs when the standing plasmon resonance coincides with the fundamental dipole mode of the ungated portion of the channel.

The nonlinear oscillations of field and current in semiconductor superlattices excited by terahertz laser radiation are studied within a self-consistent multifrequency internal field approach. We show that the oscillatory character of the nonlinear susceptibilities and dissipative and parametric instabilities in superlattices leads to multivaluedness and hysteresis of their spectral harmonics as functions of the external field amplitude. The key mechanisms of such spectral behavior are the spontaneous generation of a static field and parametric creation and amplification of the external field harmonics and subharmonics. It is shown that the field inside the superlattice cannot be understood in terms of a single frequency, especially for superlattices having high electron concentration.

We analyze a simple model of a quantum cell composed of two Coulomb-coupled double dot systems with one electron in each double dot. The interaction of electrons with acoustic phonons is considered as the principal mechanism that relaxes the cell to the ground state. Non-Markovian stochastic equations for population differences and dipole moments of the constituent double dots are derived. It is found that in order for the bistable state of the quantum cell to exist, the effective energy of Coulomb repulsion between the double dot systems must exceed the individual tunnel splitting energy, as well as the phonon temperature. The behavior of the cell polarization near the critical temperature is described analytically. We calculate the damping rates determining cell relaxation to its minimum-energy state and discuss limitations on the speed of cell response to external fields caused by the finite relaxation time.

The dynamics of the temporal formation of high electric field domains in a one-dimensional superlattice miniband subject to inelastic phonon scattering is analyzed here. Our formulation is based on the derivation of equations of motion for generating functions of electron momentum fluctuations which take account of electron scattering by acoustic phonons, facilitating the determination of analytical expressions for both the electron drift velocity and the diffusion coefficient as functions of the applied bias voltage. The speed of domain formation and the minimum carrier concentration required are determined explicitly.

We have examined the effects of inelastic phonon scattering on the lead-to-lead current through a parallel-quantum-double-dot device to determine the persistence of coherence within the device. The tunnel-coupled double-dot system is taken to be symmetric and is threaded by Aharonov–Bohm magnetic flux. We show that at resonant values of the magnetic flux, when only the bonding or antibonding state is involved in transport through the double dot, the current–voltage characteristic changes drastically and the electron–phonon interaction has a pronounced effect on the level populations. However, it does not destroy coherence during the tunneling process through the system.

The frequency‐dependence of the carrier drift velocity in superlattice miniband conduction in response to a small signal ac electric field is investigated for laterally unconfined and one‐dimensionally confined (2D) superlattices biased in the negative differential mobility regime. Numerical calculations show that in both systems there exists a mobility‐transition frequency of order of 100 GHz, above which the differential mobility becomes positive. This frequency in a 2D superlattice is about three times that in an unconfined system, owing to enhanced carrier scattering. In a domain‐driven microwave oscillator, the mobility‐transition frequency is expected to be relatively small compared to the oscillator frequency. Nonetheless, the higher mobility‐transition frequency in the 2D superlattice would render it more advantageous for use in negative differential mobility microwave oscillators.

The effect of a transverse electric field on Fano line shapes in electronic transport through a quantum wire is investigated via a Feshbach three-channel model. The coupling between channels is provided by an attractive short-range scatterer with lateral extent. It is shown that the resonance structure in a particular subband is sensitive on the electric field strength and direction. In particular, collapse of a Fano profile either in the first or the second subband may occur, depending on whether the electric field points in the negative or positive direction, respectively. This is due to the vanishing coupling between the bound states and the conduction ones which, in turn, is a consequence of the electric field-induced shift of the confining potential. This tunability of Fano resonances may prove experimentally useful in ballistic transport through narrow channels. The results in the first subband are compared with those obtained from a two-channel model. A detailed account of the transmission phase is...

We analyze the effects of a distortion of the nuclear potential of a molecular quantum dot (QD), as well as a shift of its equilibrium position, on nonequilibrium-vibration-assisted tunneling through the QD with a single level ($\epsilon_d$) coupled to the vibrational mode. For this purpose, we derive an explicit analytical expression for the Franck-Condon (FC) factor for a displaced-distorted oscillator surface of the molecule and establish rate equations in the joint electron-phonon representation to examine the current-voltage characteristics and zero-frequency shot noise, and skewness as well. Our numerical analyses shows that the distortion has two important effects. The first one is that it breaks the symmetry between the excitation spectra of the charge states, leading to asymmetric tunneling properties with respect to $\epsilon_d>0$ and $\epsilon_d, Comment: 29 pages, 11 figures, published version