Validity of t–J approximation for extended Hubbard model with strong repulsion

Abstract

It is shown that for finite cyclic systems described by two band Hubbard Hamiltonian with strong electron repulsion the reduction to effective t-J model may give incorrect description of the ground state symmetry due to neglect of the correlated hopping terms.

Quantum phase transitions in skewed ladder systems

“…An example is the change in GS of a one-dimensional extended Hubbard model from a spin density wave state to a bond order wave state or from a bond order wave state to a charge density wave state. 1–6 Best known model Hamiltonians exhibiting quantum phase transitions are the one-dimensional Hubbard 7,8 and long range Hubbard models (also known as the Pariser–Parr–Pople models) 9,10 and the Heisenberg spin chains with competing interactions. 11–32 The Hubbard model was invented to study itinerant electron magnetism and has been the cornerstone for studying electron correlations in metallic systems.…”