3,521 research outputs found
Canted Antiferromagnetic Order of Imbalanced Fermi-Fermi mixtures in Optical Lattices by Dynamical Mean-Field Theory
We investigate antiferromagnetic order of repulsively interacting fermionic
atoms in an optical lattice by means of Dynamical Mean-Field Theory (DMFT).
Special attention is paid to the case of an imbalanced mixture. We take into
account the presence of an underlying harmonic trap, both in a local density
approximation and by performing full Real-Space DMFT calculations. We consider
the case that the particle density in the trap center is at half filling,
leading to an antiferromagnetic region in the center, surrounded by a Fermi
liquid region at the edge. In the case of an imbalanced mixture, the
antiferromagnetism is directed perpendicular to the ferromagnetic polarization
and canted. We pay special attention to the boundary structure between the
antiferromagnetic and the Fermi liquid phase. For the moderately strong
interactions considered here, no Stoner instability toward a ferromagnetic
phase is found. Phase separation is only observed for strong imbalance and
sufficiently large repulsion.Comment: 7 pages, 5 figures, published versio
Self-Consistent Theory of Anderson Localization: General Formalism and Applications
The self-consistent theory of Anderson localization of quantum particles or
classical waves in disordered media is reviewed. After presenting the basic
concepts of the theory of Anderson localization in the case of electrons in
disordered solids, the regimes of weak and strong localization are discussed.
Then the scaling theory of the Anderson localization transition is reviewed.
The renormalization group theory is introduced and results and consequences are
presented. It is shown how scale-dependent terms in the renormalized
perturbation theory of the inverse diffusion coefficient lead in a natural way
to a self-consistent equation for the diffusion coefficient. The latter
accounts quantitatively for the static and dynamic transport properties except
for a region near the critical point. Several recent applications and
extensions of the self-consistent theory, in particular for classical waves,
are discussed.Comment: 25 pages, 2 figures; published version including correction
Microscopic conditions favoring itinerant ferromagnetism: Hund's rule coupling and orbital degeneracy
The importance of Hund's rule coupling for the stabilization of itinerant
ferromagnetism is investigated within a two-band Hubbard model. The magnetic
phase diagram is calculated by finite-temperature quantum Monte Carlo
simulations within the dynamical mean-field theory. Ferromagnetism is found in
a broad range of electron fillings whereas antiferromagnetism exists only near
half filling. The possibility of orbital ordering at quarter filling is also
analyzed.Comment: 5 pages, 6 figures, RevTeX, final version contains an additional
phase diagram for smaller Hund's rule coupling. to appear in Eur. Phys. J. B
(1998
Superfluid Helium 3: Link between Condensed Matter Physics and Particle Physics
The discovery of the superfluid phases of Helium 3 in 1971 opened the door to
one of the most fascinating systems known in condensed matter physics.
Superfluidity of Helium 3, originating from pair condensation of Helium 3
atoms, turned out to be the ideal testground for many fundamental concepts of
modern physics, such as macroscopic quantum phenomena, (gauge-)symmetries and
their spontaneous breakdown, topological defects, etc. Thereby the superfluid
phases of Helium 3 enriched condensed matter physics enormously. In particular,
they contributed significantly - and continue to do so - to our understanding
of various other physical systems, from heavy fermion and high-Tc
superconductors all the way to neutron stars, particle physics, gravity and the
early universe. A simple introduction into the basic concepts and questions is
presented.Comment: 11 pages, 2 figures; to be published in Acta Physica Polonica B
[Proceedings of the XL Jubilee Cracow School of Theoretical Physics on
"Quantum Phase Transitions in High Energy and Condensed Matter Physics"; 3-11
June, 2000, Zakopane, Poland
Ferromagnetism and non-local correlations in the Hubbard model
We study the possibility and stability of band-ferromagnetism in the
single-band Hubbard model for the simple cubic (SC) lattice. A non-local
self-energy is derived within a modified perturbation theory. Results for the
spectral density and quasiparticle density of states are shown with special
attention to the effects of k-dependence. The importance of non-local
correlations for the fulfillment of the Mermin-Wagner theorem is our main
result. A phase digram showing regions of ferromagnetic order is calculated for
the three dimensional lattice. Besides, we show results for the optical
conductivity and prove that already the renormalized one-loop contribution to
the conductivity cancels the Drude peak exactly in case of a local self-energy
which is not anymore true for a non-local self-energy.Comment: 11 pages, 10 figures, accepted for publication in PR
Anderson impurity in a correlated conduction band
We investigate the physics of a magnetic impurity with spin 1/2 in a
correlated metallic host. Describing the band by a Hubbard Hamiltonian, the
problem is analyzed using dynamical mean-field-theory in combination with
Wilson's nonperturbative numerical renormalization group. We present results
for the single-particle density of states and the dynamical spin susceptibility
at zero temperature. New spectral features (side peaks) are found which should
be observable experimentally. In addition, we find a general enhancement of the
Kondo scale due to correlations. Nevertheless, in the metallic phase, the Kondo
scale always vanishes exponentially in the limit of small hybridization.Comment: Final version, 4 pages RevTeX, 8 eps figures include
T-matrix formulation of real-space dynamical mean-field theory and the Friedel sum rule for correlated lattice fermions
We formulate real-space dynamical mean-field theory within scattering theory.
Thereby the Friedel sum rule is derived for interacting lattice fermions at
zero temperature.Comment: 7 pages, no figures, extended and corrected versio
Spectral properties and isotope effect in strongly interacting systems: Mott-Hubbard insulator and polaronic semiconductor
We study the electronic spectral properties in two examples of strongly
interacting systems: a Mott-Hubbard insulator with additional electron-boson
interactions, and a polaronic semiconductor. An approximate unified framework
is developed for the high energy part of the spectrum, in which the electrons
move in a random field determined by the interplay between magnetic and bosonic
fluctuations. When the boson under consideration is a lattice vibration, the
resulting isotope effect on the spectral properties is similar in both cases,
being strongly temperature and energy dependent, in qualitative agreement with
recent photoemission experiments in the cuprates.Comment: Refs. added, revised introduction and conclusio
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