Electron-electron Interactions and 4kf Localization In the Bechgaard Salts and Their Sulfur Analogs - A Spectroscopic Outlook

We present the main results of a comparative study of the room temperature infrared reflectance and conductivity spectra of four representative slightly dimerized quarter-filled molecular conductors: (TMTSF)2ClO4, (TMTSF)2PF6, (TMTTF)2Br, and (TMTTF)2PF6. Our analysis based on a 1D dimerized molecular chain model assuming strong on-site correlation (U) has been successful in explaining the relation between the variation of the spectral features and of the amplitude of the stack dimerization in the above series. The results indicate that a narrow 4k(F) dimerization gap opens at the Fermi level in all the studied materials.