83 research outputs found
Interplay of the pseudogap and the BCS gap for heteropairs in K-Li mixture
The description of heteropairs like K-Li near and in the
superconducting state requires a fully selfconsistent theory [see Hanai and
Ohashi, Phys. Rev. A 90, 043622 (2014)]. We derive analytic pseudogap Green's
functions for the "normal" and superconducting states from the Luttinger-Ward
theory with the T-matrix in the static separable approximation. The
self-consistency in the closing loop of self-energy has two pronounced effects
on the single-particle spectrum. First, the single-particle excitations decay
before the asymptotic quasiparticle propagation is established, therefore the
normal state is not a Fermi liquid. Second, the pseudogap has a V shape even
for s-wave pairing. The V-shaped pseudogap and the U-shaped BCS gap interfere
resulting in slope breaks of the gap walls and the in-gap states in the density
of states. Various consequences of an incomplete self-consistency are
demonstrated.Comment: Published versio
Coexistence of phase transitions and hysteresis near BEC
Multiple phases occurring in a Bose gas with finite-range interaction are
investigated. In the vicinity of the onset of Bose-Einstein condensation (BEC)
the chemical potential and the pressure show a van-der-Waals like behavior
indicating a first-order phase transition although there is no long-range
attraction. Furthermore the equation of state becomes multivalued near the BEC
transition. For a Hartree-Fock or Popov (Hartree-Fock-Bogoliubov) approximation
such a multivalued region can be avoided by the Maxwell construction. For
sufficiently weak interaction the multivalued region can also be removed using
a many-body \mbox{T-matrix} approximation. However, for strong interactions
there remains a multivalued region even for the \mbox{T-matrix} approximation
and after the Maxwell construction, what is interpreted as a density
hysteresis. This unified treatment of normal and condensed phases becomes
possible due to the recently found scheme to eliminate self-interaction in the
\mbox{T-matrix} approximation, which allows to calculate properties below and
above the critical temperature.Comment: Phys. Rev. A 87, 053617 (2013) [7 pages
Phase diagram and binding energy of interacting Bose gases
From the many-body T-matrix the condition for a medium-dependent bound state
and its binding energy is derived for a homogeneous interacting Bose gas. This
condition provides the critical line in the phase diagram in terms of the
medium-dependent scattering length. Separating the Bose pole from the
distribution function the influence of a Bose condensate is discussed and a
thermal minimum of the critical scattering length is found
Femtosecond formation of collective modes due to meanfield fluctuations
Starting from a quantum kinetic equation including the mean field and a
conserving relaxation-time approximation we derive an analytic formula which
describes the time dependence of the dielectric function in a plasma created by
a short intense laser pulse. This formula reproduces universal features of the
formation of collective modes seen in recent experimental data of femtosecond
spectroscopy. The presented formula offers a tremendous simplification for the
description of the formation of quasiparticle features in interacting systems.
Numerical demanding treatments can now be focused on effects beyond these gross
features found here to be describable analytically.Comment: 4 pages 3 figures, PRB in pres
Enhancement of pairing due to the presence of resonant cavities
A correlated fermion system is considered surrounding a finite cavity with
virtual levels. The pairing properties are calculated and the influence of the
cavity is demonstrated. To this end the Gell-Mann and Goldberger formula is
generalized to many-body systems. We find a possible enhancement of pairing
temperature if the Fermi momentum times the cavity radius fulfills a certain
resonance condition which suggests an experimental realization.Comment: 4 pages 2 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
The concept of correlated density and its application
The correlated density appears in many physical systems ranging from dense
interacting gases up to Fermi liquids which develop a coherent state at low
temperatures, the superconductivity. One consequence of the correlated density
is the Bernoulli potential in superconductors which compensates forces from
dielectric currents. This Bernoulli potential allows to access material
parameters. Though within the surface potential these contributions are largely
canceled, the bulk measurements with NMR can access this potential. Recent
experiments are explained and new ones suggested. The underlying quantum
statistical theory in nonequilibrium is the nonlocal kinetic theory developed
earlier.Comment: 14 pages, CMT30 proceeding
Nonlocal Kinetic Equation and Simulations of Heavy Ion Reactions
A kinetic equation which combines the quasiparticle drift of Landau's
equation with a dissipation governed by a nonlocal and noninstantaneous
scattering integral in the spirit of Enskog corrections is discussed. Numerical
values of the off-shell contribution to the Wigner distribution, of the
collision duration and of the collision nonlocality are presented for different
realistic potentials. On preliminary results we show that simulations of
quantum molecular dynamics extended by the nonlocal treatment of collisions
leads to a broader proton distribution bringing the theoretical spectra closer
towards the experimental values than the local approach.Comment: Proceedings of the Erice School, published as Vol. 42 of "Progress in
Particle and Nuclear Physics" by ELSEVIE
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