On the spectral relations for multitime correlation functions

A general approach for derivation of the spectral relations for the multitime correlation functions is presented. A special attention is paid to the consideration of the non-ergodic (conserving) contributions and it is shown that such contributions can be treated in a rigorous way using multitime temperature Green functions. Representation of the multitime Green functions in terms of the spectral densities and solution of the reverse problem -- finding of the spectral densities from the known Green functions are given for the case of the three-time correlation functions.Comment: 12 pages, submitted to the special issue of the Condensed Matter Physics journal devoted to the Green's functions metho

Effect of correlated hopping on thermoelectric properties: Exact solutions for the Falicov-Kimball model

The effect of correlated hopping on the charge and heat transport is investigated for the Falicov-Kimball model. Exact solutions for the electrical and thermal conductivities and thermoelectric power are obtained within the dynamical mean field theory. The temperature dependences of the transport coefficients are analysed for particular values of correlated hopping which correspond to the significant reconstruction of the density of states and transport function. The cases with strong enhancement of thermoelectric properties are elucidated.Comment: 14 pages, 8 figure

Dynamical susceptibilities in strong coupling approach: General scheme and Falikov-Kimball model

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: 6 pages, lecture given at the 2nd International Pamporovo Workshop on Cooperative Phenomena in Condensed Matter (28th July - 7th August 2001, Pamporovo, Bulgaria

Strong coupling Hartree-Fock approximation in the dynamical mean-field theory

In the limit of infinite spatial dimensions a thermodynamically consistent theory, which is valid for arbitrary value of the Coulombic interaction ($U<\infty$), is built for the Hubbard model when the total auxiliary single-site problem exactly splits into four subspaces with different ``vacuum states''. Some analytical results are given for the Hartree-Fock approximation when the 4-pole structure for Green's function is obtained: two poles describe contribution from the Fermi liquid component, which is ferromagnetic and dominant for small electron and hole concentrations (``overdoped case'' of high-$T_c$'s), whereas other two describe contribution from the non-Fermi liquid, which is antiferromagnetic and dominant close to half filling (``underdoped case'').Comment: 8 pages, 3 eps figures, feynmf, submitted to Condensed Matter Physic

Nonresonant Raman and inelastic X-ray scattering in the charge-density-wave phase of the spinless Falicov-Kimball model

Nonresonant inelastic light and X-ray scattering is investigated for the spinless Falicov-Kimball model on an infinite-dimensional hypercubic lattice with a charge-density-wave phase at half filling. The many-body density of states (DOS) is found for different values of the Coulomb repulsion $U$, ranging from a dirty metal to a Mott insulator. At zero temperature, the charge gap is exactly equal to $U$; increasing the temperature rapidly fills the gap with subgap states. The nonresonant response function for Raman and inelastic X-ray scattering shows peaks connected with transitions over the gap and transitions that involve subgap states. In the case of X-ray scattering (when both energy and momentum are transferred), the response function illustrates features of dynamical screening (vertex corrections) in the different (nonresonant) symmetry channels ($A_{\rm 1g}$ and $B_{\rm 1g}$). We also derive and verify the first moment sum rules for the (nonresonant) Raman and inelastic X-ray response functions.Comment: 19 pages, 17 figure