Search

International audience; An universal fingerprint of glasses has been found in low-temperature thermodynamic properties of charge/spin density wave (C/SDW) systems. Deviations from the well-known Debye, elastic continuum prediction for specific heat (flat C-p/T-3 plot) appear as two anomalies; the upturn below 1 K and a broad bump at T similar to 10 K (named Boson peak in glasses). The first one, inherent of localized two level systems within the shalow corrugated phase space, exhibits slow relaxation with the complex dynamics. The second one, "Boson peak-like peak" was attributed to the pinned mode and incomplete softening of CDW superstructural mode. We discuss similar C-p(T) features found also in incommensurate dielectrics with well documented soft-mode anomalies.

Probing charge density wave system (CDW) o-TaS3 with dielectric spectroscopy reveals two processes determined by the CDW phase dynamics, one of which (-process) freezes at finite glass transition temperature TG at which there is less then one free carrier per phase coherence domain [1]. Irradiating the samples by 2 MeV protons we introduced interstitials and vacancies in the lattice, uniformly throughout the sample. We have observed gradual decrease of amplitude of the -process upon increasing the radiation dose, along with an increase of TG, while the other (-process) has been left unchanged. Increase of TG depends on the irradiation dose, and consequently on the domain size, in the activated manner (see Figure). It follows closely the temperature dependence of free carrier density, which does not change with the irradiation. Our results confirm previously suggested freezing criterion for CDW phase [1]. [1] D. Starešinić et. al. Phys. Rev. B 65 (2002) 165109.

Thin granular films of charge density wave (CDW) system K0.3MoO3 were prepared by pulsed laser deposition and investigated by various standard characterization methods such as GI-XRD, electric transport, TOF-ERDA, AFM and UV-vis spectroscopy. While all these methods indicate that the thin films consist of nanometer grains of K0.3MoO3, it is only the non-destructive femtosecond time-resolved spectroscopy (fsTRS) that demonstrates the charge density wave nature of the ground state and therefore proves directly the presence of K0.3MoO3. Furthermore, the comparison of the fsTRS data obtained in thin films and in single crystals shows the reduction of the charge density wave transition temperature and of the photoinduced signal strength in granular thin films in respect to single crystals, which is attributed to the granularity and crystal growth morphology. Our results establish fsTRS technique as the indispensible tool for the detection and characterization of complex ground states in nano-sized systems. Photoinduced reflectivity transients in a) bulk K0.3MoO3 and b) thin film of K0.3MoO3 on Al2O3 substrate as a function of temperature recorded at the same excitation density.