121 research outputs found
Lifetime of the surface magnetoplasmons in metallic nanoparticles
We study the influence of an external magnetic field on the collective
electronic excitations in metallic nanoparticles. While the usual surface
plasmon corresponding to the collective oscillation of the electrons with
respect to the ionic background persists in the direction parallel to the
magnetic field, the components in the perpendicular plane are affected by the
field and give rise to two collective modes with field-dependent frequencies,
the surface magnetoplasmons. We analyze the decay of these collective
excitations by their coupling to particle-hole excitations and determine how
their lifetimes are modified by the magnetic field. In particular, we show that
the lifetime of the usual surface plasmon is not modified by the magnetic
field, while the lifetime of the two surface magnetoplasmons present a weak
magnetic-field dependence. Optical spectroscopy experiments are suggested in
which signatures of the surface magnetoplasmons may be observed.Comment: 11 pages, 6 figures; published versio
Two interacting particles in a disordered chain IV: Scaling of level curvatures
The curvatures of two-particle energy levels with respect to the enclosed
magnetic flux in mesoscopic disordered rings are investigated numerically. We
find that the typical value of the curvatures is increased by interactions in
the localised regime and decreased in the metallic regime. This confirms a
prediction by Akkermans and Pichard (Eur. Phys. J. B 1, 223 (1998)). The
interaction-induced changes of the typical curvatures at different energies and
disorder strengths exhibit one-parameter scaling with a conductance-like single
parameter. This suggests that interactions could influence the conductance of
mesoscopic systems similarly.Comment: 9 pages, 7 figures. Other parts of the series: cond-mat/9706258,
cond-mat/9801134, cond-mat/980813
Delocalization due to correlations in two-dimensional disordered systems
We study the spectral statistics of interacting spinless fermions in a
two-dimensional disordered lattice. Within a full quantum treatment for small
few-particle-systems, we compute the low-energy many-body states numerically.
While at weak disorder the interactions reduce spectral correlations and lead
to localization, for the case of strong disorder we find that a moderate
Coulomb interaction has a delocalizing effect. In addition, we observe a
non-universal structure in the level-spacing distribution which we attribute to
a mechanism reinforcing spectral correlations taking place in small systems at
strong disorder.Comment: 6 pages, 4 figures, corrected typo
Persistent currents for Coulomb interacting electrons on 2d disordered lattices: Sign and interaction dependence in the Wigner crystal regime
A Wigner crystal structure of the electronic ground state is induced by
strong Coulomb interactions at low temperature in clean or disordered
two-dimensional (2d) samples. For fermions on a mesoscopic disordered 2d
lattice, being closed to a torus, we study the persistent current in the regime
of strong interaction at zero temperature. We perform a perturbation expansion
starting from the Wigner crystal limit which yields power laws for the
dependence of the persistent current on the interaction strength. The sign of
the persistent current in the strong interaction limit is independent of the
disorder realization and strength. It depends only on the electro-statically
determined configuration of the particles in the Wigner crystal.Comment: 13 pages, 4 figures, final version (introduction and discussion
extended
Two interacting particles in a disordered chain II: Critical statistics and maximum mixing of the one body states
For two particles in a disordered chain of length with on-site
interaction , a duality transformation maps the behavior at weak interaction
onto the behavior at strong interaction. Around the fixed point of this
transformation, the interaction yields a maximum mixing of the one body states.
When (the one particle localization length), this mixing
results in weak chaos accompanied by multifractal wave functions and critical
spectral statistics, as in the one particle problem at the mobility edge or in
certain pseudo-integrable billiards. In one dimension, a local interaction can
only yield this weak chaos but can never drive the two particle system to full
chaos with Wigner-Dyson statistics.Comment: Second paper of a serie of four, to appear in Eur. Phys.
Interacting electron systems between Fermi leads: effective one-body transmissions and correlation clouds
In order to extend the Landauer formulation of quantum transport to
correlated fermions, we consider a spinless system in which charge carriers
interact, connected to two reservoirs by non-interacting one-dimensional leads.
We show that the mapping of the embedded many-body scatterer onto an effective
one-body scatterer with interaction-dependent parameters requires to include
parts of the attached leads where the interacting region induces power law
correlations. Physically, this gives a dependence of the conductance of a
mesoscopic scatterer upon the nature of the used leads which is due to electron
interactions inside the scatterer. To show this, we consider two identical
correlated systems connected by a non-interacting lead of length
. We demonstrate that the effective one-body transmission of the
ensemble deviates by an amount from the behavior obtained
assuming an effective one-body description for each element and the combination
law of scatterers in series. is maximum for the interaction strength
around which the Luttinger liquid becomes a Mott insulator in the used model,
and vanishes when and . Analogies with the Kondo
problem are pointed out.Comment: 5 pages, 6 figure
Partial local density of states from scanning gate microscopy
Scanning gate microscopy images from measurements made in the vicinity of
quantum point contacts were originally interpreted in terms of current flow.
Some recent work has analytically connected the local density of states to
conductance changes in cases of perfect transmission, and at least
qualitatively for a broader range of circumstances. In the present paper, we
show analytically that in any time-reversal invariant system there are
important deviations that are highly sensitive to imperfect transmission.
Nevertheless, the unperturbed partial local density of states can be extracted
from a weakly invasive scanning gate microscopy experiment, provided the
quantum point contact is tuned anywhere on a conductance plateau. A
perturbative treatment in the reflection coefficient shows just how sensitive
this correspondence is to the departure from the quantized conductance value
and reveals the necessity of local averaging over the tip position. It is also
shown that the quality of the extracted partial local density of states
decreases with increasing tip radius.Comment: 16 pages, 9 figure
From ballistic motion to localization: a phase space analysis
We introduce phase space concepts to describe quantum states in a disordered
system. The merits of an inverse participation ratio defined on the basis of
the Husimi function are demonstrated by a numerical study of the Anderson model
in one, two, and three dimensions. Contrary to the inverse participation ratios
in real and momentum space, the corresponding phase space quantity allows for a
distinction between the ballistic, diffusive, and localized regimes on a unique
footing and provides valuable insight into the structure of the eigenstates.Comment: 4 pages, 3 figures, RevTeX
Disordered Systems in Phase Space
As a function of the disorder strength in a mesoscopic system, the electron
dynamics crosses over from the ballistic through the diffusive towards the
localized regime. The ballistic and the localized situation correspond to
integrable or regular behavior while diffusive conductors correspond to chaotic
behavior. The chaotic or regular character of single wave functions can be
inferred from phase space concepts like the Husimi distribution and the Wehrl
entropy. These quantities provide useful information about the structure of
states in disordered systems. We investigate the phase space structure of one
dimensional (1d) and 2d disordered systems within the Anderson model. The Wehrl
entropy of the eigenstates allows to detect the crossover between the
ballistic, diffusive and localized regime.Comment: 4 pages, requires annmod.cls (included). A version with full
resolution figures is available from
http://www.physik.uni-augsburg.de/theo1/ingold/e/publrev.htm
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