Direct Measurement of One-Dimensional Plasmon Dispersion and Damping

Plasmons in the one-dimensional organic metal tetrathiafulvalene-tetracyanoquinodimethane were directly measured by high-energy inelastic electron scattering in thin crystalline films at 300°K. For plasmons propagating along the conducting $b$ axis the plasmon energy decreases from 0.75 to 0.55 eV and the width increases linearly as the plasmon momentum increases. Plasmons at 45° to $b$ have an energy of 0.6 eV and show no dispersion.