Electron-electron interactions in the fulvalene family of organic metals

Magnetic susceptibility as well as optical reflectivity data in the metallic regime of the conductivity of HMTTF-TCNQ are presented. It is shown that: 1. (1) The spin susceptibility of the donor stack is temperature independent in the temperature range of the metallic conductivity 50 ≤T≤300 K. 2. (2) By comparing the magnitude of this susceptibility with the value estimated from plasma frequency measurements based on the model of non-interacting electrons, we conclude that the donor stack susceptibility is not enhanced. 3. (3) A comparison of data on the three compounds (HMTTF, TTF, TSeF)-TCNQ leads to the conclusion that the donor stack susceptibility is enhanced only in TTF-TCNQ. © 1977.