Comments on the metallic conductivity of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ)

The anomalously large pressure dependence of the conductivity of tetrathiafulvalenium-tetracyanoquinodimethanide and some related charge-transfer salts is discussed. It appears to be ten times larger than the pressure dependence of the one-electron bandwidth and thus is not easily understood in terms of single-particle scattering processes. It also gives an important contribution to the temperature dependence of the conductivity and probably all other Fermi-level properties via the effect of thermal expansion.