Fermionic SK-models with Hubbard interaction: Magnetism and electronic structure

Details Fermionic SK-models with Hubbard interaction: Magnetism and electronic structure Fermionic SK-models with Hubbard interaction: Magnetism and electronic structure

2002-07-31

arxiv.org/abs/cond-mat/0207734v1

Physics

Condensed Matter

Disordered Systems and Neural Networks

29 pages, 26 Figures, 4 jpeg- and 3 gif-Fig-files included

Scientific paper

10.1103/PhysRevB.67.245111

Models with range-free frustrated Ising spin- and Hubbard interaction are treated exactly by means of the discrete time slicing method. Critical and tricritical points, correlations, and the fermion propagator, are derived as a function of temperature T, chemical potential \mu, Hubbard coupling U, and spin glass energy J. The phase diagram is obtained. Replica symmetry breaking (RSB)-effects are evaluated up to four-step order (4RSB). The use of exact relations together with the 4RSB-solutions allow to model exact solutions by interpolation. For T=0, our numerical results provide strong evidence that the exact density of states in the spin glass pseudogap regime obeys \rho(E)=const |E-E_F| for energies close to the Fermi level. Rapid convergence of \rho'(E_F) under increasing order of RSB is observed. The leading term resembles the Efros-Shklovskii Coulomb pseudogap of localized disordered fermionic systems in 2D. Beyond half filling we obtain a quadratic dependence of the fermion filling factor on the chemical potential. We find a half filling transition between a phase for U>\mu, where the Fermi level lies inside the Hubbard gap, into a phase where \mu(>U) is located at the center of the upper spin glass pseudogap (SG-gap). For \mu>U the Hubbard gap combines with the lower one of two SG-gaps (phase I), while for \mu