337 research outputs found
Phase Transitions of Fermions Coupled to a Gauge Field: a Quantum Monte Carlo Approach
A grand canonical system of non-interacting fermions on a square lattice is
considered at zero temperature. Three different phases exist: an empty lattice,
a completely filled lattice and a liquid phase which interpolates between the
other two phases. The Fermi statistics can be changed into a Bose statistics by
coupling a statistical gauge field to the fermions. Using a quantum Monte Carlo
method we investigate the effect of the gauge field on the critical properties
of the lattice fermions. It turns out that there is no significant change of
the phase diagram or the density of particles due to the gauge field even at
the critical points. This result supports a recent conjecture by Huang and Wu
that certain properties of a three-dimensional flux line system (which is
equivalent to two-dimensional hard-core bosons) can be explained with
non-interacting fermion models.Comment: 12 pages, Plain-Tex, 5 figure
Pair-tunneling resonance in the single-electron transport regime
We predict a new electron pair-tunneling (PT) resonance in non-linear
transport through quantum dots with positive charging energies exceeding the
broadening due to thermal and quantum fluctuations. The PT resonance shows up
in the single-electron transport (SET) regime as a peak in the derivative of
the non-linear conductance when the electrochemical potential of one electrode
matches the average of two subsequent charge addition energies. For a single
level quantum dot (Anderson model) we find the analytic peak shape and the
dependence on temperature, magnetic field and junction asymmetry and compare
with the inelastic cotunneling peak which is of the same order of magnitude. In
experimental transport data the PT resonance may be mistaken for a weak SET
resonance judging only by the voltage dependence of its position. Our results
provide essential clues to avoid such erroneous interpretation of transport
spectroscopy data.Comment: 5 pages, 2 figures, published versio
Phase Diagram of the Hubbard Model: Beyond the Dynamical Mean Field
The Dynamical Cluster Approximation (DCA) is used to study non-local
corrections to the dynamical mean field phase diagram of the two-dimensional
Hubbard model. Regions of antiferromagnetic, d-wave superconducting,
pseudo-gapped non-Fermi liquid, and Fermi liquid behaviors are found, in rough
agreement with the generic phase diagram of the cuprates. The non-local
fluctuations beyond the mean field both suppress the antiferromagnetism and
mediate the superconductivity.Comment: 4 pages, 5 eps figures, submitted to PR
Strongly enhanced shot noise in chains of quantum dots
We study charge transport through a chain of quantum dots. The dots are fully
coherent among each other and weakly coupled to metallic electrodes via the
dots at the interface, thus modelling a molecular wire. If the non-local
Coulomb interactions dominate over the inter-dot hopping we find strongly
enhanced shot noise above the sequential tunneling threshold. The current is
not enhanced in the region of enhanced noise, thus rendering the noise
super-Poissonian. In contrast to earlier work this is achieved even in a fully
symmetric system. The origin of this novel behavior lies in a competition of
"slow" and "fast" transport channels that are formed due to the differing
non-local wave functions and total spin of the states participating in
transport. This strong enhancement may allow direct experimental detection of
shot noise in a chain of lateral quantum dots.Comment: 4 pages, 2 figures, submitted to PR
Keep Food Lockers Working!
Frozen assets are a mighty good thing to have- when the assets are meats, vegetables and fruits. And they can be important to war effort by helping to provide an adequate and nutritious year-round food supply
Super-poissonian noise, negative differential conductance, and relaxation effects in transport through molecules, quantum dots and nanotubes
We consider charge transport through a nanoscopic object, e.g. single
molecules, short nanotubes, or quantum dots, that is weakly coupled to metallic
electrodes. We account for several levels of the molecule/quantum dot with
level-dependent coupling strengths, and allow for relaxation of the excited
states. The current-voltage characteristics as well as the current noise are
calculated within first-order perturbation expansion in the coupling strengths.
For the case of asymmetric coupling to the leads we predict
negative-differential-conductance accompanied with super-poissonian noise. Both
effects are destroyed by fast relaxation processes. The non-monotonic behavior
of the shot noise as a function of bias and relaxation rate reflects the
details of the electronic structure and level-dependent coupling strengths.Comment: 8 pages, 7 figures, submitted to Phys. Rev. B, added reference
Stretching Our Meat Supply
Meatless days and rationing may be “just around the corner,” but they need be no hardship for the American homemaker. Her only question will be “ What alternates will supply the same food value as meat?
- …