107 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
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
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
Intermediate Regime between the Fermi Glass and the Mott Insulator in one Dimension
We consider the ground state reorganization driven by an increasing nearest
neighbor repulsion U for spinless fermions in a strongly disordered ring. When
U -> 0, the electrons form a glass with Anderson localized states. At half
filling, a regular array of charges (Mott insulator) is pinned by the random
substrate when U -> \infty. Between those two insulating limits, we show that
there is an intermediate regime where the electron glass becomes more liquid
before crystallizing. The liquid-like behavior of the density-density
correlation function is accompanied by an enhancement of the persistent
current.Comment: 5 pages, Latex, uses moriond.sty (included), Contribution to the
Proceedings of the Rencontres de Moriond 199
From the Fermi glass towards the Mott insulator in one dimension: Delocalization and strongly enhanced persistent currents
When a system of spinless fermions in a disordered mesoscopic ring becomes
instable between the inhomogeneous configuration driven by the random potential
(Anderson insulator) and the homogeneous one driven by repulsive interactions
(Mott insulator), the persistent current can be enhanced by orders of
magnitude. This is illustrated by a study of the change of the ground state
energy under twisted boundary conditions using the density matrix
renormalization group algorithm.Comment: 4 pages, 5 figures; RevTe
Delocalization effects and charge reorganizations induced by repulsive interactions in strongly disordered chains
We study the delocalization effect of a short-range repulsive interaction on
the ground state of a finite density of spinless fermions in strongly
disordered one dimensional lattices. The density matrix renormalization group
method is used to explore the charge density and the sensitivity of the ground
state energy with respect to the boundary condition (the persistent current)
for a wide range of parameters (carrier density, interaction and disorder).
Analytical approaches are developed and allow to understand some mechanisms and
limiting conditions. For weak interaction strength, one has a Fermi glass of
Anderson localized states, while in the opposite limit of strong interaction,
one has a correlated array of charges (Mott insulator). In the two cases, the
system is strongly insulating and the ground state energy is essentially
invariant under a twist of the boundary conditions. Reducing the interaction
strength from large to intermediate values, the quantum melting of the solid
array gives rise to a more homogeneous distribution of charges, and the ground
state energy changes when the boundary conditions are twisted. In individual
chains, this melting occurs by abrupt steps located at sample-dependent values
of the interaction where an (avoided) level crossing between the ground state
and the first excitation can be observed. Important charge reorganizations take
place at the avoided crossings and the persistent currents are strongly
enhanced around the corresponding interaction value. These large delocalization
effects become smeared and reduced after ensemble averaging. They mainly
characterize half filling and strong disorder, but they persist away of this
optimal condition.Comment: 18 pages, 15 figures, accepted for publication in Eur. Phys. J.
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