Eur. Phys. J. B (2012) 85: 253
https://doi.org/10.1140/epjb/e2012-30306-9

Regular Article

Ferromagnetism in the asymmetric Hubbard model

Institute of Experimental Physics, Slovak Academy of Sciences Watsonova 47, 04353 Košice, Slovakia

^a e-mail: farky@saske.sk

Received: 11 April 2012
Received in final form: 6 June 2012
Published online: 30 July 2012

Abstract

The density matrix renormalization group and quantum Monte Carlo calculations are used to study ferromagnetism in the one- and two-dimensional asymmetric Hubbard model. The model is examined for a wide range of electron concentrations n, Coulomb interactions U and down-spin electron hopping integrals t_↓ changing from t_↓ = 0 (the case of the Falicov-Kimball model) to t_↓ = 1 (the case of the conventional Hubbard model). The critical value of the down-spin electron hopping integral t_↓^c below which the ferromagnetic state becomes stable is calculated numerically and the ground-state phase diagram of the model (in the t_↓-U plane) is presented for physically the most interesting cases (n = 1/4,1/2 and 3/4). It is shown that at fixed U the ferromagnetic state is stabilized with increasing concentration of holes (1 − n) in the system, and at fixed n the ferromagnetic state is generally stabilized with increasing U.