Spin order and orbital disorder in LaTiO3

Abstract A mechanism for the removal of orbital degeneracy in LaTiO 3 is proposed. Assuming an antiferromagnetic spin ordering (presumably induced by some deviations from the fully symmetric Kugel–Khomskii (KK) model Hamiltonian), we show that the two-magnon excitations play a crucial role in the formation of the orbital liquid. The strongly damped orbital excitations (orbitons) merge into a common continuum with the spin excitations. As a result, the orbital dynamics do modify the stiffness of the spin waves but do not participate as a separate branch of excitations in the low-temperature thermodynamics. Therefore, the direct experimental observation of the orbital dynamics at low temperatures is hardly possible.