Magnetic interactions and optical spectral weights in Mott insulators with orbital degrees of freedom

We outline a unified approach to magnetic and optical properties of Mott insulators at orbital degeneracy, which provides deep insight into the complex spin–orbital physics. It introduces partial sum rules for individual optical excitations which follow from the multiplet structure of transition metal ions. We show that the observed anisotropies and the temperature dependence of the optical spectral weights in LaVO 3 and LaMnO 3 follow from spin and orbital correlations and are well understood within this approach. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)