Single-Crystal Reflectance Studies of Tetrathiafulvalene Tetracyanoquinodimethane

Abstract

The polarized reflectance of single crystals of tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) at 300 K is reported over the frequency range 300 to 4000 ${\mathrm{cm}}^{-1\mathrm{}}$, with unpolarized data extending to 50 ${\mathrm{cm}}^{-1\mathrm{}}$. A Kramers-Kronig analysis is used to obtain the frequency-dependent conductivity ${\sigma }_1\left(\omega \right)$ and dielectric function, ${\epsilon }_1\left(\omega \right)$, for both $a$ and $b$ crystallographic axes. The results establish the existence of the energy gap and provide a quantitative measurement of the oscillator strength and relaxation time of the collective mode.