Spin Dynamics and Orbital State inLaTiO3

A neutron scattering study of the Mott-Hubbard insulator ${\mathrm{LaTiO}}_3$ ( $T_N=132\mathrm{K}$) reveals a spin wave spectrum that is well described by a nearest-neighbor superexchange constant $J=15.5\mathrm{meV}$ and a small Dzyaloshinskii-Moriya interaction ( $D=1.1\mathrm{meV}$). The nearly isotropic spin wave spectrum is surprising in view of the absence of a static Jahn-Teller distortion that could quench the orbital angular momentum, and it may indicate strong orbital fluctuations. A resonant x-ray scattering study has uncovered no evidence of orbital order in ${\mathrm{LaTiO}}_3$.