Phase transitions in an extended hubbard model

Publisher Website
Google Scholar
Abstract
We derive the free energy functional of an extended Hubbard model Hamiltonian with interatomic interactions. One has to solve a four coupled fields (two vectorial spin fields and two scalar charge fields) problem. Two are potentially soft (one spin and one charge field). We show that as far as the ferromagnetic transition is concerned, universality holds and that introducing a short range interaction between neighbours yields the same free energy functional as for the simple Hubbard model if irrelevant coupling terms are discarded. For the charge ordered transition we show using renormalization group theory arguments that the spin-charge coupling is irrelevant and that the coupling between the two charge fields can give rise to a first or second order transition depending on the details of the metallic band structure and the value of the interaction energy parameters