Hexamethylene-tetrathiafulvalenium tetracyanoquinodimethanide as a prototype of a quasi-one-dimensional organic conductor

Decomposition of the magnetic susceptibility of hexamethylene-tetrathiafulvalenium tetracyanoquinodimethanide (HMTTF-TCNQ) to donor and acceptor contributions yields the following results: (i) The spin susceptibility of the donor stack is temperature independent in the temperature range of the metallic conductivity 50≤T≤300 K. (ii) The acceptor stack susceptibility exhibits in the same temperature range a pronounced temperature dependence. (iii) The magnitude of the acceptor stack susceptibility is vanishingly small at the metal-insulator transition temperature. These findings are interpreted in terms of a broad temperature range of Peierls fluctuations on the acceptor stacks.