2,325 research outputs found
Dynamical susceptibilities in strong coupling approach
A general scheme to calculate dynamical susceptibilities of strongly
correlated electron systems within the dynamical mean field theory is
developed. Approach is based on an expansion over electron hopping around the
atomic limit (within the diagrammatic technique for site operators: projection
and Hubbard ones) in infinite dimensions. As an example, the Falicov-Kimball
and simplified pseudospin-electron models are considered for which an
analytical expressions for dynamical susceptibilities are obtained.Comment: 2 pages, 3 eps figures, final version published in proceedings of
M2S-HTSC-VI (Houston
Dynamical mean-field theory for the normal phase of the attractive Hubbard model
We analyze the normal phase of the attractive Hubbard model within dynamical
mean-field-theory. We present results for the pair-density, the
spin-susceptibility, the specific heat, the momentum distribution, and for the
quasiparticle weight. At weak coupling the low-temperature behavior of all
quantities is consistent with Fermi liquid theory. At strong coupling all
electrons are bound pairs, which leads to a spin gap and removes fermionic
quasi-particle excitations. The transition between the Fermi liquid phase and
the pair phase takes place at a critical coupling of the order of the
band-width and is generally discontinuous at sufficiently low temperatures
Volume fraction variations and dilation in colloids and granulars
Discusses the importance of spatial and temporal variations in particle volume fraction to understanding the force response of concentrated colloidal suspensions and granular materials
Spin lifetimes and strain-controlled spin precession of drifting electrons in zinc blende type semiconductors
We study the transport of spin polarized electrons in n-GaAs using spatially
resolved continuous wave Faraday rotation. From the measured steady state
distribution, we determine spin relaxation times under drift conditions and, in
the presence of strain, the induced spin splitting from the observed spin
precession. Controlled variation of strain along [110] allows us to deduce the
deformation potential causing this effect, while strain along [100] has no
effect. The electric field dependence of the spin lifetime is explained
quantitatively in terms of an increase of the electron temperature.Comment: 5 pages, 6 figure
Exact analytic results for the Gutzwiller wave function with finite magnetization
We present analytic results for ground-state properties of Hubbard-type
models in terms of the Gutzwiller variational wave function with non-zero
values of the magnetization m. In dimension D=1 approximation-free evaluations
are made possible by appropriate canonical transformations and an analysis of
Umklapp processes. We calculate the double occupation and the momentum
distribution, as well as its discontinuity at the Fermi surface, for arbitrary
values of the interaction parameter g, density n, and magnetization m. These
quantities determine the expectation value of the one-dimensional Hubbard
Hamiltonian for any symmetric, monotonically increasing dispersion epsilon_k.
In particular for nearest-neighbor hopping and densities away from half filling
the Gutzwiller wave function is found to predict ferromagnetic behavior for
sufficiently large interaction U.Comment: REVTeX 4, 32 pages, 8 figure
Pseudogap at hot spots in the two-dimensional Hubbard model at weak coupling
We analyze the interaction-induced renormalization of single-particle
excitations in the two-dimensional Hubbard model at weak coupling using the
Wick-ordered version of the functional renormalization group. The self energy
is computed for real frequencies by integrating a flow equation with
renormalized two-particle interactions. In the vicinity of hot spots, that is
points where the Fermi surface intersects the umklapp surface, self energy
effects beyond the usual quasi-particle renormalizations and damping occur near
instabilities of the normal, metallic phase. Strongly enhanced renormalized
interactions between particles at different hot spots generate a pronounced
low-energy peak in the imaginary part of the self energy, leading to a
pseudogap-like double-peak structure in the spectral function for
single-particle excitations.Comment: 14 pages, 7 figure
Correlated hopping of electrons: Effect on the Brinkman-Rice transition and the stability of metallic ferromagnetism
We study the Hubbard model with bond-charge interaction (`correlated
hopping') in terms of the Gutzwiller wave function. We show how to express the
Gutzwiller expectation value of the bond-charge interaction in terms of the
correlated momentum-space occupation. This relation is valid in all spatial
dimensions. We find that in infinite dimensions, where the Gutzwiller
approximation becomes exact, the bond-charge interaction lowers the critical
Hubbard interaction for the Brinkman-Rice metal-insulator transition. The
bond-charge interaction also favors ferromagnetic transitions, especially if
the density of states is not symmetric and has a large spectral weight below
the Fermi energy.Comment: 5 pages, 3 figures; minor changes, published versio
Observation Uncertainty in Reversible Markov Chains
In many applications one is interested in finding a simplified model which captures the essential dynamical behavior of a real life process. If the essential dynamics can be assumed to be (approximately) memoryless then a reasonable choice for a model is a Markov model whose parameters are estimated by means of Bayesian inference from an observed time series. We propose an efficient Monte Carlo Markov Chain framework to assess the uncertainty of the Markov model and related observables. The derived Gibbs sampler allows for sampling distributions of transition matrices subject to reversibility and/or sparsity constraints. The performance of the suggested sampling scheme is demonstrated and discussed for a variety of model examples. The uncertainty analysis of functions of the Markov model under investigation is discussed in application to the identification of conformations of the trialanine molecule via Robust Perron Cluster Analysis (PCCA+)
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