2000/05/17 by Hideo Hasegawa
Physics and Astronomy · #cond-mat.str-el
published as Foundations of Physics 30 (2000) 2061 · 14 pages, 1 figure
arxiv created 2000/05/17 · arxiv updated 2009/11/30
The mean-field theory with the use of the slave-boson functional method is generalized to take account of the spin- and orbital-ordered state in the doubly degenerate Hubbard model. Some numerical calculations are presented of the antiferromagnetic orbital-ordered state in the half-filled simple-cubic model. The orbital order in the present theory is much reduced compared with that in the Hartree-Fock approximation because of the large orbital fluctuations. From a comparison of the ground-state energy, the antiferromagnetic orbital state is shown to be unstable against the antiferromagnetic spin state, although the situation becomes reversed when the exchange interaction is \it negative.