6,488 research outputs found
Distribution of parametric conductance derivatives of a quantum dot
The conductance G of a quantum dot with single-mode ballistic point contacts
depends sensitively on external parameters X, such as gate voltage and magnetic
field. We calculate the joint distribution of G and dG/dX by relating it to the
distribution of the Wigner-Smith time-delay matrix of a chaotic system. The
distribution of dG/dX has a singularity at zero and algebraic tails. While G
and dG/dX are correlated, the ratio of dG/dX and is independent
of G. Coulomb interactions change the distribution of dG/dX, by inducing a
transition from the grand-canonical to the canonical ensemble. All these
predictions can be tested in semiconductor microstructures or microwave
cavities.Comment: 4 pages, RevTeX, 3 figure
Nonequilibrium theory of Coulomb blockade in open quantum dots
We develop a non-equilibrium theory to describe weak Coulomb blockade effects
in open quantum dots. Working within the bosonized description of electrons in
the point contacts, we expose deficiencies in earlier applications of this
method, and address them using a 1/N expansion in the inverse number of
channels. At leading order this yields the self-consistent potential for the
charging interaction. Coulomb blockade effects arise as quantum corrections to
transport at the next order. Our approach unifies the phase functional and
bosonization approaches to the problem, as well as providing a simple picture
for the conductance corrections in terms of renormalization of the dot's
elastic scattering matrix, which is obtained also by elementary perturbation
theory. For the case of ideal contacts, a symmetry argument immediately allows
us to conclude that interactions give no signature in the averaged conductance.
Non-equilibrium applications to the pumped current in a quantum pump are worked
out in detail.Comment: Published versio
Voltage-probe and imaginary potential models for dephasing in a chaotic quantum dot
We compare two widely used models for dephasing in a chaotic quantum dot: The
introduction of a fictitious voltage probe into the scattering matrix and the
addition of an imaginary potential to the Hamiltonian. We identify the limit in
which the two models are equivalent and compute the distribution of the
conductance in that limit. Our analysis explains why previous treatments of
dephasing gave different results. The distribution remains non-Gaussian for
strong dephasing if the coupling of the quantum dot to the electron reservoirs
is via ballistic single-mode point contacts, but becomes Gaussian if the
coupling is via tunneling contacts.Comment: 9 pages, RevTeX, 6 figures. Mistake in Eq. (35) correcte
Sediment Characterization of Coastal Lagoons and Bays, Virginian Province
Sediment characterizations for the following estuaries and rivers: Chesapeake Bay Potomac River Rappahannock River York River James River Chester River Choptank Rive
ADULT MOVEMENT AND LARVAL DISPERSAL OF ARGYROZONA ARGYROZONA (PISCES: SPARIDAE) FROM A TEMPERATE MARINE PROTECTED AREA
Adult emigration and larval dispersal of carpenter Argyrozona argyrozona from the Tsitsikamma National Park (TNP), South Africa, were investigated using mark-recapture data and Acoustic Doppler Current Profiler measurements of currents. Tagging data showed that adult carpenter were mainly resident, with a small proportion (7%) leaving the TNP in both easterly and westerly directions. There was no relationship between fish movement patterns and fish size or time-at-liberty. Current patterns suggest that eggs and larvae spawned within the TNP are mainly transported eastwards towards established nursery grounds; the median estimated distance moved was 299 km (range 42–561 km) in 30 days (time to flexion). Given this pattern of ichthyoplankton dispersal, together with the fact that adult carpenter within the TNP displayed a high degree of residency and that they are much more abundant than in adjacent fishing grounds (catch per unit effort being 23 times greater), it appears that the TNP protects a viable carpenter spawner population capable of seeding adjacent fishing grounds
Finite size effects and localization properties of disordered quantum wires with chiral symmetry
Finite size effects in the localization properties of disordered quantum
wires are analyzed through conductance calculations. Disorder is induced by
introducing vacancies at random positions in the wire and thus preserving the
chiral symmetry. For quasi one-dimensional geometries and low concentration of
vacancies, an exponential decay of the mean conductance with the wire length is
obtained even at the center of the energy band. For wide wires, finite size
effects cause the conductance to decay following a non-pure exponential law. We
propose an analytical formula for the mean conductance that reproduces
accurately the numerical data for both geometries. However, when the
concentration of vacancies increases above a critical value, a transition
towards the suppression of the conductance occurs.
This is a signature of the presence of ultra-localized states trapped in
finite regions of the sample.Comment: 5 figures, revtex
Effect of inelastic scattering on parametric pumping
Pumping of charge in phase-coherent mesoscopic systems due to the
out-of-phase modulation of two parameters has recently found considerable
interest. We investigate the effect of inelastic processes on the adiabatically
pumped current through a two terminal mesoscopic sample. We find that the loss
of coherence does not suppress the pumped charge but rather an additional
physical mechanism for an incoherent pump effect comes into play. In a fully
phase incoherent system the pump effect is similar to a rectification effect
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