Effect of Spin-Orbit Interaction in LaTiO_3

概要

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LaTiO_3 is a Mott insulator with a G-type antiferromagnetic ordered ground state and a Neel temperature about 135 K. Recently, Keimer et al. have shown that t_<2g> orbital degrees of freedom of Ti^<3+> are missing in LaTiO_3, although the crystal field acting on Ti^<3+> is nearly cubic. In addition to that, magnon spectra observed in neutron scattering experiments are fitted well by a spin-half isotropic Heisenberg model on a cubic lattice. Nevertheless, no evidence of static orbital order was observed in anomalous x-ray scattering experiment. To explain the quenching of the orbital degrees of freedom is one of the stimulating problems in this material. Using exact diagonalizations of finite clusters, we study the interplay of spin-orbit interactions and superexchange in the Kugel-Khomskii model of LaTiO_3. Spin-orbit interaction leads to a non degenerate ground state. However, the Kugel-Khomskii model with spin-orbit interaction does not describe well the spectrum observed in neutron scattering.
理論物理学刊行会の論文
2002-06-28