Charge-density-wave paraconductivity

The dynamic conductivity and permittivity spectra of K0.3MoO3 and (TaSe4)2I single crystals in the conducting phase (above 180 K and 260 K, respectively) have been measured, for the first time, over a broad frequency range 1 – 105 cm−1, using a combination of different spectroscopic techniques. In both compounds clearly pronounced excitations are discovered in the spectra below 50 cm−1 for the electric field parallel the chains, the direction along which the charge density wave develops at low T. We associate these excitations with charge-density-wave fluctuations which exist even at room temperature and give a collective contribution to the conductivity. For the transverse polarization, E perpendicular to the chains, a usual single-particle Drude behavior of the conductivity and permittivity spectra is observed. The experiments give clear evidence for important deviations from conventional metallic behavior in the fluctuating region, below TMF but above TCDW, the temperature where long range order develops.