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harge Density Glass - From Fictions to Fascinating Facts

30 years ago, in his paper on the interplay between the commensurability pinning and impurity pinning in 1D CDW (charge density wave), H. J. Fukuyama predicted that CDW-CDG (charge density glass) transition should be also expected as a function of the temperature [1]. We brought the experimental evidences that the real glass transition into the CDG phase occurs at a finite temperature and moreover that it is the generic feature of DW systems [2]. As pinning and screening are responsible for the glassy behaviour, CDG has a very special position in the field of glasses and it can be used as a playground for the investigation of the real nature of the glass transition, one of remaining enigmas in solid state physics. The dynamics of the CDW-CDG dielectric glass transition strongly resembles the scenario of the freezing in supercooled liquids (SCL) [2], however relevant degrees of freedom concern the CDW superstructure on characteristic scales of the size of the phase coherence length. These scales are of the order of microns, compared to few nanometers of SCL short–range order. It is shown that the glass transition temperature into CDG depends on the size of the phase coherent domains [3]. The glassy phenomenology is completed with low-energy excitations (LEE), long-time energy relaxation and aging found at low-T and a peak in heat capacity (Cp/T3). This peak resembles the boson peak (BP) in glasses and we show that pinning resonance can be assumed as a BP equivalent. Finally, one more peculiarity of CDG: LEEs of this new glassy state demonstrate very rich and unexpected magnetic properties [4]. [1] Fukuyama, H. J. Phys. Soc. Jpn 45, 1474 (1978) [ [2] Starešinić, D. et al. Phys. Rev. B 65, 165109 (2002) ; ibid, Phys. Rev. B 69, 113102 (2004) [3] Dominko, D. et al. this conference [4] Starešinić, D. et al. and Remenyi, G. et al. this conference

charge density waves; pining; comensurability

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