1,271 research outputs found
Non-linear Resistivity of a Two-Dimensional Electron Gas in a Magnetic Field
We develop a theory of nonlinear response to an electric field of a
two-dimensional electron gas (2DEG) placed in a classically strong magnetic
field. The latter leads to a non-linear current-voltage characteristic at a
relatively weak electric field. The origin of the non-linearity is two-fold:
the formation of a non-equilibrium electron distribution function, and the
geometrical resonance in the inter-Landau-levels transitions rates. We find the
dependence of the current-voltage characteristics on the electron relaxation
rates in the 2DEG.Comment: 4 pages, 2 figure
Imaging Transport Resonances in the Quantum Hall Effect
We use a scanning capacitance probe to image transport in the quantum Hall
system. Applying a DC bias voltage to the tip induces a ring-shaped
incompressible strip (IS) in the 2D electron system (2DES) that moves with the
tip. At certain tip positions, short-range disorder in the 2DES creates a
quantum dot island in the IS. These islands enable resonant tunneling across
the IS, enhancing its conductance by more than four orders of magnitude. The
images provide a quantitative measure of disorder and suggest resonant
tunneling as the primary mechanism for transport across ISs.Comment: 4 pages, 4 figures, submitted to PRL. For movies and additional
infomation, see http://electron.mit.edu/scanning/; Added scale bars to
images, revised discussion of figure 3, other minor change
The spectral form factor is not self-averaging
The spectral form factor, k(t), is the Fourier transform of the two level
correlation function C(x), which is the averaged probability for finding two
energy levels spaced x mean level spacings apart. The average is over a piece
of the spectrum of width W in the neighborhood of energy E0. An additional
ensemble average is traditionally carried out, as in random matrix theory.
Recently a theoretical calculation of k(t) for a single system, with an energy
average only, found interesting nonuniversal semiclassical effects at times t
approximately unity in units of {Planck's constant) /(mean level spacing). This
is of great interest if k(t) is self-averaging, i.e, if the properties of a
typical member of the ensemble are the same as the ensemble average properties.
We here argue that this is not always the case, and that for many important
systems an ensemble average is essential to see detailed properties of k(t). In
other systems, notably the Riemann zeta function, it is likely possible to see
the properties by an analysis of the spectrum.Comment: 4 pages, RevTex, no figures, submitted to Phys. Rev. Lett., permanent
e-mail address, [email protected]
A new Proposal for a Quasielectron Trial Wavefunction for the FQHE on a Disk
In this letter, we propose a new quasielectron trial wavefunction for
interacting electrons in two dimensions moving in a strong magnetic field in a
disk geometry. Requiring that the trial wavefunction exhibits the correct
filling factor of a quasielectron wavefunction, we obtain angular
momentum eigenfunctions. The expectation values of the energy are calculated
and compared with the data of an exact numerical diagonalization.Comment: 8 page
Sublattice ordering in a dilute ensemble of defects in graphene
Defects in graphene, such as vacancies or adsorbents attaching themselves to
carbons, may preferentially take positions on one of its two sublattices, thus
breaking the global lattice symmetry. This leads to opening a gap in the
electronic spectrum. We show that such a sublattice ordering may spontaneously
occur in a dilute ensemble defects, due to the long-range interaction between
them mediated by electrons. As a result sublattice-ordered domains may form,
with electronic properties characteristic of a two-dimensional topological
insulator.Comment: to appear in Europhysics Letter
Magnetic oscillations in planar systems with the Dirac-like spectrum of quasiparticle excitations II: transport properties
The quantum magnetic oscillations of electrical (Shubnikov de Haas effect)
and thermal conductivities are studied for graphene which represents a
distinctive example of planar systems with a linear, Dirac-like spectrum of
quasiparticle excitations. We show that if a utmost care was taken to separate
electron and phonon contributions in the thermal conductivity, the oscillations
of electron thermal conductivity, and the Lorenz number,
would be observable in the low field (less than a few Teslas) regime.Comment: 11 pages, RevTeX4, 6 EPS figures; 2 references, 1 figure and one more
section are added; final version published in PR
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