Temperature dependence of optical spectral weights in quarter-filled ladder systems

The temperature dependence of the integrated optical conductivity I(T) reflects the changes of the kinetic energy as spin and charge correlations develop. We calculated I(T) in the frame of a t-J-V model for ladder systems, such as α′-NaV2O5, and show that the measured strong T dependence of I(T) for NaV2O5 can be explained by the destruction of short-range antiferromagnetic correlations. Thus I(T) provides detailed information about the T dependence of superexchange energy and thereby allows for an independent determination of magnetic energy scales.