Spin waves, scattering at 4kF, and spin-Peierls fluctuations in an organic metal: Tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ)

An interpretation is given for recent diffuse x-ray and neutron scattering experiments on tetrathiafulvalene-tetracyanoquinodimethane using a model of strong Coulomb interactions. The diffuse x-ray scattering observed at q=0.59b* (4kF) is identified as quasielastic scattering from a charge-density wave which is driven by long-range Coulomb interactions, while the scattering at q=0.295b* (2kF) is due to a Kohn anomaly caused by spin-Peierls fluctuations. Three experiments are proposed in order to verify this interpretation, including a search for spin waves which are predicted to be observable by inelastic neutron scattering near q=0.295b*. © 1978 The American Physical Society.