Non-perturbative ground-state of a generalized Hubbard model

Oracio Navarro, E. Flores, M. Avignon

Henry L. Neal

Giuseppe Albertini, V. E. Korepin, Andreas Schadschneider

We consider the limit of strong Coulomb attraction for generalized Hubbard models with eta -symmetry. In this limit these models are equivalent to the ferromagnetic spin- 1/2 Heisenberg quantum spin chain. In order to study the behaviour of the superconducting phase in the electronic model under perturbations which break the eta -symmetry we investigate the ground state of the ferromagnetic non-critical XXZ-chain in the sector with fixed magnetization. It turns out to be a large bound state of N magnons. We find that the perturbations considered here lead to the disappearance of the off-diagonal long-range order.

Koichi Kusakabe, Hideo Aoki

The occurrence of high-spin ground states in the strongly correlated electron system is clarified in one and two dimensions. Even for infinitesimal Hubbard U , the ground state with a spin-polarized Fermi surface periodically arises as the number of electrons is varied due to a ` k -space Hund's coupling'. A non-perturbative crossover to strong U regime, which is accompanied by a series of level crossings and involves the stability of the Nagaoka state, is also demonstrated.

U. Brandt, Joachim Stolze

ARMEN N. KOCHARIAN, Chia‐Wei Yang, Y. L. Chiang

The accurate analytical and numerical calculations of the electronic band structure and ground state properties of strongly correlated electrons within the Hubbard model are performed by constructing convergent perturbation theory for general interaction strength and electron concentration. We test the developed perturbation approach about mean field solution in the extreme conditions of one dimensionality for entire parameter space of electron interaction U/t and electron concentration n. The many-body perturbation formalism up two second order about the generalized self-consistent field (GSCF) Hamiltonian goes beyond the range of applicability of standard perturbation theory by incorporating systematically the effect of the random-phase-type perturbation techniques and controlled expansion of the energy functional for general U/t and n. The second order perturbation correction vanishes at small and large U/t limit and performed calculations of the ground state energy show a next to the perfect numerical agreement with the Bethe-ansatz results.