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

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