OPTICAL PROBING OF THERMAL LATTICE FLUCTUATIONS IN CHARGE-DENSITY-WAVE CONDENSATES

Thermal lattice fluctuations in charge-density-wave (CDW) condensates have been studied by means of optical investigations on the prototype CDW compound K0.3MoO3 and its alloys. The temperature dependence of the CDW gap absorption in the mid-IR frequency range is strongly indicative of the important role played by the thermal lattice fluctuation effects. The latter remove the inverse-square-root singularity, expected for the case of the static distorted lattice. In fact, a considerable broadening (i.e., larger than k(B)T) of the subgap tail absorption is found by increasing the temperature towards T(CDW). Moreover, we find that the phase phonon modes also give an important contribution to the disorder parameter, thus being an essential ingredient for the thermal fluctuation effects.