RUTHENIUM PYRAZINE MIXED-VALENCE CHAINS BY A 2-BAND HUBBARD HAMILTONIAN - A DISCUSSION ON OPTICAL CONDUCTIVITY SPECTRA

We have investigated the optical conductivity spectra of [Ru(pyzRu)3]m+ chain (pyz=pyrazine) through a two-band Hubbard Hamiltonian. It is shown that the main features of absorption spectra, observed experimentally for various degrees of oxidation (m), may be well reproduced within this simple model. The spectra, for different values of the relevant parameters in the most suitable range for reproducing the experimental results, have been analysed in terms of various quantities obtained from the many-particle eigenstates, in order to give a realistic assignment of the observed peaks and their dependence on the values of the parameters. It is shown that the characteristic shift of spectral weight from high to low frequency upon reduction is related to strong charge fluctuations between metallic and ligand bands.