X-Ray evidence for 2kF charge density wave instability in tetrateflurafulvalene–tetracyanoquinodimethane: TTeF–TCNQ

Abstract

We report an X-ray diffuse scattering study of the charge-transfer salt TTeF–TCNQ. This salt develops one-dimensional (1D) 2k_F charge density wave (CDW) structural fluctuations which do not condense into superlattice spots down to 20 K, the lowest temperature investigated. This observation allows a charge transfer value of ρ= 0.70 ± 0.02 to be determined, in good agreement with a previous IR spectroscopy determination. We compare these CDW structural fluctuations with those previously observed in other charge-transfer salts like TTF–TCNQ and TSF–TCNQ which undergo a Peierls transition. We suggest that the increase of donor polarizability and of donor bandwidth on going from TTF–TCNQ to TSF–TCNQ, and then to TTeF–TCNQ, makes the CDW instability different between these salts.