42 research outputs found
Spin and interaction effects on charge distribution and currents in one-dimensional conductors and rings within the Hartree-Fock approximation
Using the self--consistent Hartree-Fock approximation for electrons with spin
at zero temperature, we study the effect of the electronic interactions on the
charge distribution in a one-dimensional continuous ring containing a single
scatterer. We reestablish that the interaction suppresses the decay
of the Friedel oscillations. Based on this result, we show that in an infinite
one dimensional conductor containing a weak scatterer, the current is totally
suppressed because of a gap opened at the Fermi energy. In a canonical ensemble
of continuous rings containing many scatterers, the interactions enhance the
average and the typical persistent current.Comment: 5 pages, 4 figure
Does the attractive Hubbard model support larger persistent currents than the repulsive one ?
We consider a one-dimensional Hubbard model in the presence of disorder. We
compute the charge stiffness for a mesoscopic ring, as a function of the size
, which is a measure of the permanent currents. We find that for finite
disorder the permanent currents of the system with repulsive interactions are
larger than those of the system with attractive interactions. This counter
intuitive result is due to the fact that local density fluctuations are reduced
in the presence of repulsive interactions.Comment: 14 pages; Revtex 3.0; 3 postscript figures uuencoded with uufile
Interacting electrons in disordered potentials: Conductance versus persistent currents
An expression for the conductance of interacting electrons in the diffusive
regime as a function of the ensemble averaged persistent current and the
compressibility of the system is presented. This expression involves only
ground-state properties of the system. The different dependencies of the
conductance and persistent current on the electron-electron interaction
strength becomes apparent. The conductance and persistent current of a small
system of interacting electrons are calculated numerically and their variation
with the strength of the interaction is compared. It is found that while the
persistent current is enhanced by interactions, the conductance is suppressed.Comment: REVTeX, 4 pages, 3 figures, all uuencoded, accepted for publication
in PR
Enhanced Charge and Spin Currents in the One-Dimensional Disordered Mesoscopic Hubbard Ring
We consider a one-dimensional mesoscopic Hubbard ring with and without
disorder and compute charge and spin stiffness as a measure of the permanent
currents. For finite disorder we identify critical disorder strength beyond
which the charge currents in a system with repulsive interactions are {\em
larger} than those for a free system. The spin currents in the disordered
repulsive Hubbard model are enhanced only for small , where the magnetic
state of the system corresponds to a charge density wave pinned to the
impurities. For large , the state of the system corresponds to localized
isolated spins and the spin currents are found to be suppressed. For the
attractive Hubbard model we find that the charge currents are always suppressed
compared to the free system at all length scales.Comment: 20 RevTeX 3.0 pages, 8 figures NOT include
The interplay between electron-electron interactions and impurities in one-dimensional rings
The persistent current and charge stiffness of a one-dimensional Luttinger
liquid on a ring threaded by a magnetic flux are calculated by Monte Carlo
simulation. By changing the random impurity potential strength and the
electron-electron interaction, we see a crossover behavior between weak and
strong impurity limits. For weak impurity potentials, interactions enhance
impurity effects, that is, interactions decrease the current and the stiffness.
On the other hand, interactions tend to screen impurities when the impurity
potential is strong. Temperature dependence of the persistent current and the
charge stiffness shows a peak at a characteristic temperature, consistent with
a recent single impurity study.Comment: 4 pages (ReVTeX3.0) + 3 figures (in uuencoded postscript format)
appended in the end of the fil
Short-range repulsion and isospin dependence in the KN system
The short-range properties of the KN interaction are studied within the
meson-exchange model of the Juelich group. Specifically, dynamical explanations
for the phenomenological short-range repulsion, required in this model for
achieving agreement with the empirical KN data, are explored. Evidence is found
that contributions from the exchange of a heavy scalar-isovector meson
(a_0(980)) as well as from genuine quark-gluon exchange processes are needed.
Taking both mechanisms into account a satisfactory description of the KN phase
shifts can be obtained without resorting to phenomenological pieces.Comment: 26 pages, 5 figure
Coulomb drag in mesoscopic rings
We develop a Luttinger liquid theory of the Coulomb drag of persistent
currents flowing in concentric mesoscopic rings, by incorporating non-linear
corrections to the electron dispersion relation. We demonstrate that at low
temperatures, interactions between electrons in different rings generate an
additional phase and thus alter the period of Aharonov-Bohm oscillations. The
resulting nondissipative drag depends strongly on the relative parity of the
electron numbers. We also show that interactions set a new temperature scale
below which the linear response theory does not apply at certain values of
external flux.Comment: Latex 10 pages + 2 Figure
Pion-nucleon scattering in a meson-exchange model
The pi-N interaction is studied within a meson-exchange model and in a
coupled-channels approach which includes the channels pi-N, eta-N, as well as
three effective pi-pi-N channels namely rho-N, pi-Delta, and sigma-N. Starting
out from an earlier model of the Julich group systematic improvements in the
dynamics and in some technical aspects are introduced. With the new model an
excellent quantitative reproduction of the pi-N phase shifts and inelasticity
parameters in the energy region up to 1.9 GeV and for total angular momenta J
leq 3/2 is achieved. Simultaneously, good agreement with data for the total and
differential pi-N -> eta-N transition cross sections is obtained. The
connection of the pi_N dynamics in the S_{11} partial wave with the reaction
pi-N -> eta-N is discussed.Comment: 32 pages, 9 figure
Effective-field-theory approach to persistent currents
Using an effective-field-theory (nonlinear sigma model) description of
interacting electrons in a disordered metal ring enclosing magnetic flux, we
calculate the moments of the persistent current distribution, in terms of
interacting Goldstone modes (diffusons and cooperons). At the lowest or
Gaussian order we reproduce well-known results for the average current and its
variance that were originally obtained using diagrammatic perturbation theory.
At this level of approximation the current distribution can be shown to be
strictly Gaussian. The nonlinear sigma model provides a systematic way of
calculating higher-order contributions to the current moments. An explicit
calculation for the average current of the first term beyond Gaussian order
shows that it is small compared to the Gaussian result; an order-of-magnitude
estimation indicates that the same is true for all higher-order contributions
to the average current and its variance. We therefore conclude that the
experimentally observed magnitude of persistent currents cannot be explained in
terms of interacting diffusons and cooperons.Comment: 12 pages, no figures, final version as publishe
Kaon effective mass and energy from a novel chiral SU(3)-symmetric Lagrangian
A new chiral SU(3) Lagrangian is proposed to describe the properties of kaons
and antikaons in the nuclear medium, the ground state of dense matter and the
kaon-nuclear interactions consistently.
The saturation properties of nuclear matter are reproduced as well as the
results of the Dirac-Br\"{u}ckner theory. Our numerical results show that the
kaon effective mass might be changed only moderately in the nuclear medium due
to the highly non-linear density effects. After taking into account the
coupling between the omega meson and the kaon, we obtain similar results for
the effective kaon and antikaon energies as calculated in the
one-boson-exchange model while in our model the parameters of the kaon-nuclear
interactions are constrained by the SU(3) chiral symmetry.Comment: 13 pages, Latex, 3 PostScript figures included; replaced by the
revised version, to appear in Phys. Rev.