5,022 research outputs found
Screening of electrostatic potential in a composite fermion system
Screening of the electric field of a test charge by monolayer and
double-layer composite fermion systems is considered. It is shown that the
electric field of the test charge is partly screened at distances much large
then the magnetic length. The value of screening as a function of the distance
depends considerably on the filling factor. The effect of variation of the
value of screening in the double-layer system upon a transition to a state
described by the Halperin wave function is determined.Comment: 5 pages, 2 eps figures include
Grafted Rods: A Tilting Phase Transition
A tilting phase transition is predicted for systems comprising rod like
molecules which are irreversibly grafted to a flat surface, so that the non
interacting rods are perpendicularly oriented. The transition is controlled by
the grafting density . It occurs as increases as a result of the
interplay between two energies. Tilt is favoured by the van-der-Waals
attraction between the rods. It is opposed by the bending elasticity of the
grafting functionality. The role of temperature is discussed, and the tilting
mechanism is compared to other tilting transitions reported in the literature.Comment: 21 pages, 2 figures, to appear in Journal de Physique I
Interaction of quantum Hall systems with waveguide elastic modes
An interaction of non-uniform plane elastic modes of the waveguide type with
monolayer and double-layer quantum Hall systems is considered. It is shown,
that unlike the case of the surface acoustic wave propagation, the restriction
on maximal values of the wave vectors for which the velocity shift can be
observed experimentally does not take place for the waveguide modes. In case of
study of incompressible fractional quantum Hall states the effect can be used
for measuring a dependence of the effective magnetic length on the filling
factor and for observing phase transitions in double-layer system under the
interlayer distance variationComment: 6 pages, 3 eps figures included, Fig.1 and Fig.3 correcte
Conductance beyond the Landauer limit and charge pumping in quantum wires
Periodically driven systems, which can be described by Floquet theory, have
been proposed to show characteristic behavior that is distinct from static
Hamiltonians. Floquet theory proposes to describe such periodically driven
systems in terms of states that are indexed by a photon number in addition to
the usual Hilbert space of the system. We propose a way to measure directly
this additional Floquet degree of freedom by the measurement of the DC
conductance of a single channel quantum point contact. Specifically, we show
that a single channel wire augmented with a grating structure when irradiated
with microwave radiation can show a DC conductance above the limit of one
conductance quantum set by the Landauer formula. Another interesting feature of
the proposed system is that being non-adiabatic in character, it can be used to
pump a strong gate-voltage dependent photo-current even with linearly polarized
radiation.Comment: 9 pages; 3 figures: Final published version; includes minor revisions
from the last versio
Entanglement Spectrum and Entanglement Thermodynamics of Quantum Hall Bilayers at nu=1
We study the entanglement spectra of bilayer quantum Hall systems at total
filling factor nu=1. In the interlayer-coherent phase at layer separations
smaller than a critical value, the entanglement spectra show a striking
similarity to the energy spectra of the corresponding monolayer systems around
half filling. The transition to the incoherent phase can be followed in terms
of low-lying entanglement levels. Finally, we describe the connection between
those two types of spectra in terms of an effective temperature leading to
relations for the entanglement entropy which are in full analogy to canonical
thermodynamics.Comment: New findings in Eqs.(5)-(8) and pertaining discussion, and addendum
to the title, version as publishe
The Tomonaga-Luttinger Model and the Chern-Simons Theory for the Edges of Multi-layer Fractional Quantum Hall Systems
Wen's chiral Tomonaga-Luttinger model for the edge of an m-layer quantum Hall
system of total filling factor nu=m/(pm +- 1) with even p, is derived as a
random-phase approximation of the Chern-Simons theory for these states. The
theory allows for a description of edges both in and out of equilibrium,
including their collective excitation spectrum and the tunneling exponent into
the edge. While the tunneling exponent is insensitive to the details of a
nu=m/(pm + 1) edge, it tends to decrease when a nu=m/(pm - 1) edge is taken out
of equilibrium. The applicability of the theory to fractional quantum Hall
states in a single layer is discussed.Comment: 15 page
A number conserving theory for topologically protected degeneracy in one-dimensional fermions
Semiconducting nanowires in proximity to superconductors are among promising
candidates to search for Majorana fermions and topologically protected
degeneracies which may ultimately be used as building blocks for topological
quantum computers. The prediction of neutral Majorana fermions in the
proximity-induced superconducting systems ignores number-conservation and thus
leaves open the conceptual question of how a topological degeneracy that is
robust to all local perturbations arises in a number-conserving system. In this
work, we study how local attractive interactions generate a topological
ground-state near-degeneracy in a quasi one-dimensional superfluid using
bosonization of the fermions. The local attractive interactions opens a
topological quasiparticle gap in the odd channel wires (with more than one
channel) with end Majorana modes associated with a topological near-degeneracy.
We explicitly study the robustness of the topological degeneracy to local
perturbations and find that such local perturbations result in quantum phase
slips which split of the topological degeneracy by an amount that does not
decrease exponentially with the length of the wire, but still decreases rapidly
if the number of channels is large. Therefore a bulk superconductor with a
large number of channels is crucial for true topological degeneracy.Comment: 11 pages, 2 figure
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