41,431 research outputs found
Low-energy local density of states of the 1D Hubbard model
We examine the local density of states (DOS) at low energies numerically and
analytically for the Hubbard model in one dimension. The eigenstates represent
separate spin and charge excitations with a remarkably rich structure of the
local DOS in space and energy. The results predict signatures of strongly
correlated excitations in the tunneling probability along finite quantum wires,
such as carbon nanotubes, atomic chains or semiconductor wires in scanning
tunneling spectroscopy (STS) experiments. However, the detailed signatures can
only be partly explained by standard Luttinger liquid theory. In particular, we
find that the effective boundary exponent can be negative in finite wires,
which leads to an increase of the local DOS near the edges in contrast to the
established behavior in the thermodynamic limit.Comment: 6 pages, 4 figures, more information can be found at
http://www.physik.uni-kl.de/eggert/papers/index.htm
Universal features in sequential and nonsequential two-photon double ionization of helium
We analyze two-photon double ionization of helium in both the nonsequential
and sequential regime. We show that the energy spacing between the two emitted
electrons provides the key parameter that controls both the energy and the
angular distribution and reveals the universal features present in both the
nonsequential and sequential regime. This universality, i.e., independence of
photon energy, is a manifestation of the continuity across the threshold for
sequential double ionization. For all photon energies, the energy distribution
can be described by a universal shape function that contains only the spectral
and temporal information entering second-order time-dependent perturbation
theory. Angular correlations and distributions are found to be more sensitive
to the photon energy. In particular, shake-up interferences have a large effect
on the angular distribution. Energy spectra, angular distributions
parameterized by the anisotropy parameters, and total cross sections presented
in this paper are obtained by fully correlated time-dependent ab initio
calculations.Comment: 12 pages, 8 figure
On the Integrability of Classical Ruijsenaars-Schneider Model of Type
The problem of finding most general form of the classical integrable
relativistic models of many-body interaction of the type is
considered. In the simplest nontrivial case of ,the extra integral of
motion is presented in explicit form within the ansatz similar to the
nonrelativistic Calogero-Moser models. The resulting Hamiltonian has been found
by solving the set of two functional equations.Comment: 10 pages, LaTeX2e, no figure
Two-photon Double Ionization of H in Intense Femtosecond Laser Pulses
Triple-differential cross sections for two-photon double ionization of
molecular hydrogen are presented for a central photon energy of 30 eV. The
calculations are based on a fully {\it ab initio}, nonperturbative, approach to
the time-dependent Schroedinger equation in prolate spheroidal coordinates,
discretized by a finite-element discrete-variable-representation. The wave
function is propagated in time for a few femtoseconds using the short,
iterative Lanczos method to study the correlated response of the two
photoelectrons to short, intense laser radiation. The current results often lie
in between those of Colgan {\it et al} [J. Phys. B {\bf 41} (2008) 121002] and
Morales {\it et al} [J. Phys. B {\bf 41} (2009) 134013]. However, we argue that
these individual predictions should not be compared directly to each other, but
preferably to experimental data generated under well-defined conditions.Comment: 4 pages, 4 figure
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