Abstract. We have investigated the electrodynamic

We have studied the effect of thermal lattice fluctuations on the optical properties of the chargedensity wave (CDW) condensates K03Mo03 and (TaSe4)2I. From the temperature dependence of the CDW gap absorption in the midinfrared frequency range, there is a strong indication of the important role played by the thermal lattice fluctuation and zero-point lattice motion. The latter removes the inverse square-root singularity expected for the case of a static distorted lattice. In fact, a considerable broadening (i.e. , larger than k&T) of the subgap tail absorption is found by increasing the temperature towards the transition temperature TzD~. We compare our experimental findings with the predictions of a theoretical model, which suggests that zero-point and thermal lattice motions have a similar effect on the electronic properties as disorder. Better agreement with the theory is obtained when the contribution to the disorder parameter from phase phonon modes is also taken into account.

No abstract

We have conducted optical and point-contact spectroscopy (PCS) investigations on the URuz -Re, Si, (0 c x < 0.8) system, in order to determine the absorption spectrum and to obtain a fingerprint of the density of states with respect to the magnetic ground state as x is varied, In the antiferromagnetic phase ( E < O.l), we clearly have evidence for a gap-like feature in both the absorption and PCS spectra. On the other hand, these features disappear for the ferromagnetic ground state (2 > 0.4). We discuss our experimental findings in relation to the itinerant nature of the magnetic phase transitions.

Erratum for Europhys. Lett. 32 (4) 367-372 (1995)