377 research outputs found
Momentum conservation and local field corrections for the response of interacting Fermi gases
We reanalyze the recently derived response function for interacting systems
in relaxation time approximation respecting density, momentum and energy
conservation. We find that momentum conservation leads exactly to the local
field corrections for both cases respecting only density conservation and
respecting density and energy conservation. This rewriting simplifies the
former formulae dramatically. We discuss the small wave vector expansion and
find that the response function shows a high frequency dependence of
which allows to fulfill higher order sum rules. The momentum
conservation also resolves a puzzle about the conductivity which should only be
finite in multicomponent systems
Dependence of structure factor and correlation energy on the width of electron wires
The structure factor and correlation energy of a quantum wire of thickness
are studied in random phase approximation and for the less
investigated region . Using the single-loop approximation, analytical
expressions of the structure factor have been obtained. The exact expressions
for the exchange energy are also derived for a cylindrical and harmonic wire.
The correlation energy is found to be represented by , for small
and high densities. For a pragmatic width of the wire, the correlation energy
is in agreement with the quantum Monte Carlo simulation data.Comment: Being slightly modifie
Effective mass in quasi two-dimensional systems
The effective mass of the quasiparticle excitations in quasi two-dimensional
systems is calculated analytically. It is shown that the effective mass
increases sharply when the density approaches the critical one of
metal-insulator transition. This suggests a Mott type of transition rather than
an Anderson like transition.Comment: 3 pages 3 figure
In-medium two-nucleon properties in high electric fields
The quantum mechanical two - particle problem is considered in hot dense
nuclear matter under the influence of a strong electric field such as the field
of the residual nucleus in heavy - ion reactions. A generalized
Galitskii-Bethe-Salpeter equation is derived and solved which includes
retardation and field effects. Compared with the in-medium properties in the
zero-field case, bound states are turned into resonances and the scattering
phase shifts are modified. Four effects are observed due to the applied field:
(i) A suppression of the Pauli-blocking below nuclear matter densities, (ii)
the onset of pairing occurs already at higher temperatures due to the field,
(iii) a field dependent finite lifetime of deuterons and (iv) the imaginary
part of the quasiparticle self-energy changes its sign for special values of
density and temperatures indicating a phase instability. The latter effect may
influence the fragmentation processes. The lifetime of deuterons in a strong
Coulomb field is given explicitly.Comment: ps file + 7 figures (eps
Breathing mode in an improved transport approach
The nuclear breathing-mode giant monopole resonance is studied within an
improved relativistic Boltzmann-Uehling-Uhlenbeck (BUU) transport approach. As
a new feature, the numerical treatment of ground state nuclei and their
phase-space evolution is realized with the same semiclassical energy density
functional. With this new method a very good stability of ground state nuclei
in BUU simulations is achieved. This is important in extracting clear
breathing-mode signals for the excitation energy and, in particular, for the
lifetime from transport theoretical studies including mean-field and
collisional effects.Comment: 33 pages, 11 figures, accepted for publication in Phys. Rev.
The sesquiterpene synthase PtTPS5 produces (1S,5S,7R,10R)-guaia-4(15)-en-11-ol and (1S,7R,10R)-guaia-4-en-11-ol in oomycete-infected poplar roots
Electric field dependence of pairing temperature and tunneling
Using the Bethe-Salpeter equation including high electric fields, the
dependence of the critical temperature of onsetting superconductivity on the
applied field is calculated analytically. The critical temperature of pairing
is shown to increase with the applied field strength. This is a new field
effect and could contribute to the explanation of recent experiments on field
induced superconductivity. From the field dependence of the Bethe-Salpeter
equation, the two--particle bound state solution is obtained as a resonance
with a tunneling probability analogous to the WKB solution of a single particle
confined in a potential and coupled to the electrical field.Comment: 4 pages 1 figure, revised version from 29.10.02, Rev. B in pres
Stability of condensate in superconductors
According to the BCS theory the superconducting condensate develops in a
single quantum mode and no Cooper pairs out of the condensate are assumed. Here
we discuss a mechanism by which the successful mode inhibits condensation in
neighboring modes and suppresses a creation of noncondensed Cooper pairs. It is
shown that condensed and noncondensed Cooper pairs are separated by an energy
gap which is smaller than the superconducting gap but large enough to prevent
nucleation in all other modes and to eliminate effects of noncondensed Cooper
pairs on properties of superconductors. Our result thus justifies basic
assumptions of the BCS theory and confirms that the BCS condensate is stable
with respect to two-particle excitations
Exactly solvable model of three interacting particles in an external magnetic field
The quantum mechanical problem of three identical particles, moving in a
plane and interacting pairwise via a spring potential, is solved exactly in the
presence of a magnetic field. Calculations of the pair--correlation function,
mean distance and the cluster area show a quantization of these parameters.
Especially the pair-correlation function exhibits a certain number of maxima
given by a quantum number. We obtain Jastrow pre-factors which lead to an
exchange correlation hole of liquid type, even in the presence of the
attractive interaction between the identical electrons.Comment: 8 pages 3 figure
Shifts of the nuclear resonance in the vortex lattice in YBaCuO
The NMR and NQR spectra of Cu in the CuO plane of
YBaCuO in the superconducting state are discussed in terms of the
phenomenological theory of Ginzburg-Landau type extended to lower temperatures.
We show that the observed spectra, Kumagai {\em et al.}, PRB {\bf 63}, 144502
(2001), can be explained by a standard theory of the Bernoulli potential with
the charge transfer between CuO planes and CuO chains assumed.Comment: 11 pages 7 figure
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