Specific Plateaus of the Quantum Hall Effect Induced by an Applied Bias

The spectrum and the eigenstates of a finite 2D tight-binding electronic system, with Dirichlet boundary conditions, in magnetic field and external linear potential are studied. The eigenstates show an equipotential character and may cross the plaquette in the direction perpendicular to the electric field. When leads are added to the plaquette, the channels carrying the current may be shortcut by equipotentials, resulting in additional plateaus situated inbetween the usual IQHE plateaus. This idea is confirmed by a numerical calculation within the four-terminal Landauer-B\"{u}ttiker approach.Comment: 9 pages, revtex, 2 gif figures and 5 postscript figure

Molecular Dynamics Simulations of Field Emission From a Prolate Spheroidal Tip

High resolution molecular dynamics simulations with full Coulomb interactions of electrons are used to investigate field emission from a prolate spheroidal tip. The space charge limited current is several times lower than the current calculated with the Fowler-Nordheim formula. The image-charge is taken into account with a spherical approximation, which is good around the top of the tip, i.e. region where the current is generated.Comment: 6 pages, 8 figure

Quantum analog of channeled electron trajectories in periodic magnetic and electric fields

We calculate the quantum states corresponding to the drifting and channeled classical orbits in a two-dimensional electron gas (2DEG) with strong magnetic and electric modulations along one spatial direction, $x$. The channeled states carry high, concentrated currents along the $y$ axis, and are confined in an effective potential well. The quantum and the classical states are compared.Comment: 8 pages with 4 included ps figures, contribution to "SemiMag 13" Nijmegen, August 1998, to appear in Physica

Generalized Master equation approach to mesoscopic time-dependent transport

We use a generalized Master equation (GME) formalism to describe the non-equilibrium time-dependent transport through a short quantum wire connected to semi-infinite biased leads. The contact strength between the leads and the wire are modulated by out-of-phase time-dependent functions which simulate a turnstile device. One lead is fixed at one end of the sample whereas the other lead has a variable placement. The system is described by a lattice model. We find that the currents in both leads depend on the placement of the second lead. In the rather small bias regime we obtain transient currents flowing against the bias for short time intervals. The GME is solved numerically in small time steps without resorting to the traditional Markov and rotating wave approximations. The Coulomb interaction between the electrons in the sample is included via the exact diagonalization method

Memorization of short-range potential fluctuations in Landau levels

We calculate energy spectra of a two-dimensional electron system in a perpendicular magnetic field and periodic potentials of short periods. The Coulomb interaction is included within a screened Hartree-Fock approximation. The electrostatic screening is poor and the exchange interaction amplifies the energy dispersion. We obtain, by numerical iterations, self-consistent solutions that have a hysteresis-like property. With increasing amplitude of the external potential the energy dispersion and the electron density become periodic, and they remain stable when the external potential is reduced to zero. We explain this property in physical terms and speculate that a real system could memorize short-range potential fluctuations after the potential has been turned off.Comment: 11 pages with 4 included figures, Revte

Time-dependent transport of electrons through a photon cavity

We use a non-Markovian master equation to describe the transport of Coulomb interacting electrons through an electromagnetic cavity with one quantized photon mode. The central system is a finite parabolic quantum wire that is coupled weakly to external parabolic quasi-one-dimensional leads at $t=0$. With a stepwise introduction of complexity to the description of the system and a corresponding stepwise truncation of the ensuing many-body spaces we are able to describe the time-dependent transport of Coulomb-interacting electrons through a geometrically complex central system. We take into account the full electromagnetic interaction of electrons and cavity photons without resorting to the rotating wave approximation or reduction of the electron states to two levels. We observe that the number of initial cavity photons and their polarization can have important effects on the transport properties of the system. The quasiparticles formed in the central system have a lifetime limited by the coupling to the leads and radiation processes active on a much longer timescale.Comment: RevTeX (pdf-LaTeX) 11 pages with 12 jpg-figures include

Coulomb effects on the quantum transport of a two-dimensional electron system in periodic electric and magnetic fields

The magnetoresistivity tensor of an interacting two-dimensional electron system with a lateral and unidirectional electric or magnetic modulation, in a perpendicular quantizing magnetic field, is calculated within the Kubo formalism. The influence of the spin splitting of the Landau bands and of the density of states (DOS) on the internal structure of the Shubnikov-de Haas oscillations is analyzed. The Coulomb electron - electron interaction is responsible for strong screening and exchange effects and is taken into account in a screened Hartree-Fock approximation, in which the exchange contribution is calculated self-consistently with the DOS at the Fermi level. This approximation describes both the exchange enhancement of the spin splitting and the formation of compressible edge strips, unlike the simpler Hartree and Hartree-Fock approximations, which yield either the one or the other.Comment: 20 pages, revtex, 7 ps figures, to appear in Phys. Rev.

Planar cyclotron motion in unidirectional superlattices defined by strong magnetic and electric fields: Traces of classical orbits in the energy spectrum

We compare the quantum and the classical description of the two-dimensional motion of electrons subjected to a perpendicular magnetic field and a one-dimensional lateral superlattice defined by spatially periodic magnetic and electric fields of large amplitudes. We explain in detail the complicated energy spectra, consisting of superimposed branches of strong and of weak dispersion, by the correspondence between the respective eigenstates and the ``channeled'' and ``drifting'' orbits of the classical description.Comment: 11 pages, 11 figures, to appear in Physical Review