Electron Correlations in the High-Dimension Hubbard Model

Gang Su, Bao-Heng Zhao

Arisato Kawabata

H. Hasegawa

The effect of electron correlations in the infinite-dimension (d=∞) Hubbard model at finite temperatures has been investigated with the use of a theory which was recently proposed by the present author generalizing the slave-boson functional-integral method. Sublattice magnetizations, double occupancies and band-narrowing factors are computed as functions of the interaction, U, and the temperature, T. Calculated results are exact in the limits of U→0 and U→∞, and in the limits of T=0 and T→∞ they are expected to be very accurate owing to the nature of our mean-field-type theory for infinite-dimension systems. Similarities and differences between the calculated results for d=3 and d=∞ are also discussed.

I. V. Sankar, Ashok Chatterjee

The Holstein-Hubbard model is studied in two dimensions to explore the nature of polarons as a function of hole concentration in the strong correlation regime. A series of canonical transformations is performed to obtain an effective extended Hubbard model which, in the strong on-site electron-electron correlation regime, transforms into a t-J model and is solved using the mean-field Hartree-Fock approximation (HFA). It is shown that the hopping parameter which is related to the bandwidth of the polaron is very small for low (x ≈ 0) and high (x ≈ 1) hole concentrations whereas the hopping parameter is much larger for the intermediate hole concentrations.

D.K. Ghosh

V. Janiš, D. Vollhardt

We derive the exact expression for the averaged free energy of a general class of Hubbard-type models with local, quenched disorder in the limit of high dimensions. A clear mean-field interpretation of its structure is given. Analytic results are obtained for a simplified Hubbard model with disorder. The two-particle correlation functions are shown to display a novel coupling of quantum degrees of freedom whenever genuine electron-electron correlation effects are present.