Theoretical study of the optical conductivity of α′-NaV2O5

Using finite temperature diagonalization techniques, it is shown that the quarter-filled t-J-V model on a trellis lattice structure provides a quantitative explanation of the highly anisotropic optical conductivity of the (alpha'-NaV2O5 compound. The combined effects of the short-range Coulomb interaction 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 high energy. The role of valence fluctuations is explained in terms of the domain wall excitations of an anisotropic two-dimensional Ising model in a transverse field close to criticality.