Theoretical study of the optical conductivity of alpha '-NaV2O5

Using finite temperature diagonalization techniques, it is shown that the q uarter-filled t-J-V model on a trellis lattice structure provides a quantit ative explanation of the highly anisotropic optical conductivity of the (al pha'-NaV2O5 compound. The combined effects of the short-range Coulomb inter action and valence fluctuations of V ions determine the main absorption and the fundamental gap. Interladder hopping is necessary for the explanation of the anomalous in-gap absorption and generation of spectral weight at hig h energy. The role of valence fluctuations is explained in terms of the dom ain wall excitations of an anisotropic two-dimensional Ising model in a tra nsverse field close to criticality.