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Mott transitions in the 2-band hubbard model: A coherent potential approximation study

The half-filled isotropic degenerate two-band Hubbard model is studied within coherent potential approximation. The model is characterized by an Ising-type Hunds exchange coupling, intra- and inter-orbital Coulomb parameters. We found that the band degeneracy slightly reduces the Mott-Hubbard critical value UC. We reveal that the system can have two distinct critical values for Mott-Hubbard transitions. | Communications in Physics, Vol. 22, No. 3 (2012), pp. 223-228 MOTT TRANSITIONS IN THE 2-BAND HUBBARD MODEL: A COHERENT POTENTIAL APPROXIMATION STUDY LE DUC ANH Department of Physics, Hanoi National University of Education HOANG ANH TUAN Institute of Physics, VAST Abstract. The half-filled isotropic degenerate two-band Hubbard model is studied within coherent potential approximation. The model is characterized by an Ising-type Hunds exchange coupling, intra- and inter-orbital Coulomb parameters. We found that the band degeneracy slightly reduces the Mott-Hubbard critical value UC . We reveal that the system can have two distinct critical values for Mott-Hubbard transitions. I. INTRODUCTION The one-band Hubbard model has been used as a model for a study of strongly correlated electronic systems such as transition metal, valence-mixing and hight TC materials. Several quantitative comparisons between the physics of three dimensional transition metal oxides and the one-band Hubbard model give surprisingly good agreement [1, 2]. This good agreement is questionable since, normally, the simplest description of a real system involves electrons in a two(or more)-fold degenerate level. Using slave boson (SB) technique, Hasegawa [3] showed that the band degeneracy has strong effect on the MottHubbard transitions. The critical value UC of the double degenerate case is 1.33 times larger than that of the one-band model. Furthermore, Ono, Potthoff, and Bulla with an extension of the linearized dynamical mean-field theory found a linear dependence of UC on the band degeneracy [4]. In contrast, using dynamical mean-field with iterative perturbation theory Kajueter and Kotliar [5] pointed out that the critical value UC was slightly reduced by the band degeneracy. The purpose of this report is to study Mott-Hubbard transitions in the doubly degenerate Hubbard model at half-filling using the coherent potential approximation (CPA) [6–8]. This self-consistent approximation is known to