Theoretical study of the optical conductivity ofα′−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 ${\alpha }^{\prime }-{\mathrm{NaV}}_2{\mathrm{O}}_5$ 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.