OPTICAL INVESTIGATIONS OF THE COLLECTIVE TRANSPORT IN CDW-FILMS

The complex conductivity spectra of thin films of the charge-density-w ave-compound Rb0.3MoO3 have been measured in the millimeter frequency range. The single-phase films (thickness 250 and 750 nm) of the quasi- one-dimensional metal were grown on Al2O3 by pulsed-laser deposition. Using a coherent-source (backwardwave oscillators) spectrometer in a M ach-Zehnder arrangement, the transmission coefficient and phase shift were measured continuously in the spectral range from 3 to 9 cm(-1) fo r temperatures between 6 and 300 K. Below the Peierls transition tempe rature (T-CDW = 180 K) clear evidence has been found for a mode center ed at 4.5 cm(-1), which we attribute to the collective excitations of the charge-density-wave condensate pinned at impurities. This so-calle d pinned-mode resonance has a width of 1 cm(-1) and changes only sligh tly with temperature. (C) 1998 Elsevier Science B.V. All rights reserv ed.