Optical phonon drag and variable range hopping mechanisms of thermoelectric power generation in charge density wave system o-TaS₃}

We have measured the thermoelectric power of charge density wave system $o$-TaS$_{3}$ in a wide temperature range between 10 K and 300 K. All features characteristic for charge density wave systems have been observed; strong increase below charge density transition temperature $T_{P}$, peak at $T_{M}\sim$1/2-1/3 $T_{P}$ and change of sign at lower temperatures. These features can be explained by two contributions; free carriers drag by the optical phonons with frequencies close to the density wave gap value in the peak region and above, and hopping of localized carriers of opposite charge to free carriers at low temperatures. We argue that these are common mechanisms of thermoelectric power generation in all charge density wave systems.