Quantum Magnetism and Spin Fermion Models.pdf

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arXiv:cond-mat/0208227 v1 12 Aug 2002

Spectral Properties of the
Generalized Spin-Fermion Models∗
A.L.Kuzemsky †
Bogoliubov Laboratory of Theoretical Physics,
Joint Institute for Nuclear Research,
141980 Dubna, Moscow Region, Russia.

In order to account for competition and interplay of localized
and itinerant magnetic behaviour in correlated many body systems
with complex spectra the various types of spin-fermion models have
been considered in the context of the Irreducible Green’s Functions
(IGF) approach. Examples are generalized d − f model and KondoHeisenberg model. The calculations of the quasiparticle excitation
spectra with damping for these models has been performed in the
framework of the equation- of-motion method for two-time temperature Green’s Functions within a non-perturbative approach. A unified
scheme for the construction of Generalized Mean Fields (elastic scattering corrections) and self-energy (inelastic scattering) in terms of
the Dyson equation has been generalized in order to include the presence of the two interacting subsystems of localized spins and itinerant
electrons. A general procedure is given to obtain the quasiparticle
damping in a self-consistent way. This approach gives the complete
and compact description of quasiparticles and show the flexibility and
richness of the generalized spin-fermion model concept.

International Journal of Modern Physics B13, N 20, (1999) 2573-2605
E-mail:kuzemsky@thsun1.jinr.ru ; http://thsun1.jinr.ru∼ kuzemsky