Evidence for an additional energy scale in the frequency correlation of waves transmitted through a disordered slab

We calculate the freqency correlation function in a disordered slab using the usual diagrammatic approximation and compare our results to numerical simulations. As long as the decay width of the system is much bigger than the Thouless energy the two methods agree. Once the decay width is of order of the Thouless energy discrepancies in the half-width of the correlation function as well as in the tail regions appear. This behavior indicates the importance of the decay width in determining transport properties of disordered systems.