Damir Starešinić

Low-temperature thermodynamic investigation of the sulphur organic salts (TMTTF)2PF6 and (TMTTF)2Br (TMTTF?tetramethyltetrathiafulvalene): I. General aspects

A detailed thermodynamical investigation of the quasi-one-dimensional sulphur-based organic salts (TMTTF)2PF6 and (TMTTF)2Br is presented in the temperature range from 30 mK to 7 K. In this part (part I), we consider the general aspects of the low-temperature specific heat of these materials in relationship with their ground states and we compare them with those previously measured for selenium members of the same family. All these compounds exhibit very similar thermodynamical behaviour, despite a variety of electronic ground states: spin-Peierls for (TMTTF)2PF6, commensurate antiferromagnetic spin modulation for (TMTTF)2Br, incommensurate spin-density wave for (TMTSF)2PF6 (TMTSF≡tetramethyltetraselenafulvalene). We show that the low-energy excitations which are predominant below 1 K have a similar character to that observed in glassy systems, at least on short timescales of measurements. The dynamical aspects of the non-equilibrium thermodynamics will be presented separately in the following part (part II).

Glass transition from a slush to a real glass in charge-density-wave compound TaS3

Abstract We have found by broad-band dielectric spectroscopy of charge density wave (CDW) compound TaS 3 that the main relaxation time representing CDW viscosity shows a critical slowing down in the range 55-50 K. At lower temperatures two additional processes appear that we assign to the defects in CDW superlattice. Based on very strong similarity with the glass transition in supercooled liquids, we propose a consistent scenario of the glass transition from a CDW slush to a real CDW glass. The length/time scales involved imply the existence of a new family of glasses in systems with the long-range order such as CDW.

Looking for footprint of bulk metallic glass in electronic and phonon heat capacities of Cu55Hf45−xTix alloys

We report on the heat capacity investigation of Cu55Hf45−xTix metallic glasses. The most appropriate procedure to estimate low temperature electronic and phonon contributions has been determined. Both contributions exhibit monotonous Ti concentration dependence, demonstrating that there is no relation of either the electron density of states at the Fermi level or the Debye temperature to the increased glass forming ability in the Ti concentration range x = 15–30. The thermodynamic parameters (e.g., reduced glass temperature) remain better indicators in assessing the best composition for bulk metallic glass formation.

Detection of charge density wave ground state in granular thin films of blue bronze K0.3MoO3 by femtosecond spectroscopy

During the last years, femtosecond time-resolved spectroscopy (fsTRS) has become an important new tool to investigate low energy excitations in strongly correlated systems. By studying energy relaxation pathways linking various degrees of freedom (e.g., electrons, spin, or lattice), the interaction strengths between different subsystems can be deduced. Here we report on yet another application of fsTRS, where the technique is used to unambiguously determine the nature of the ground state in granular thin films of a prototype charge density wave system blue bronze, K0.3MoO3. These, potassium blue bronze, films, obtained for the first time ever, have been prepared by pulsed laser deposition and investigated by various standard characterization methods. While the results of all used methods indicate that the thin films consist of nanometer grains of K0.3MoO3, it is only the non-destructive fsTRS that demonstrates the charge density wave nature of the ground state. Furthermore, the comparison of the fsTRS dat...

The amorphous nature of C60 hard carbon manifested in its specific heat, sound velocity and heat conduction

Detaile dm easurements of the specific heat, thermal conductivity and relative variation of the sound velocity in the temperature range 2–280 K for hard fullerene-based carbon are reported. Th en ovel mate rial was obtained from pressure–temperature treatment of C60 fullerene and is known for a unique combination of its diamond-like hardness and high electrical conductivity. The substance was found to possess an unconventional, close-to-linear temperature dependence of the thermal conductivity over almost the entire temperature range. The specific heat of hard carbon exhibited a very large linear contribution to the specific heat at low temperatures, but no excess contribution to Cp/T 3 , and a deviation from the Debye dependence above 6 K. The sound velocity decreased linearly from 4 up to 120 K. Thes er esu lts are consistent with the concept of a glassy solid formed by polymerized and partially transformed fullerene clusters.

Thermal conductivity of hard carbon prepared from C60 fulleren

We report measurements of thermal conductivity in 30–350 K range of hard fullerene-based carbon. The material has been prepared from C60 fullerene under pressure and has an unusual combination of large hardness and relatively high electrical conductivity. Its thermal conductivity is about 5.5 W/mk at room temperature and decreases almost linearly in the investigated temperature range. The data obtained bear resemblance to the thermal properties of amorphous materials. It is consistent with the structural investigation that allows one to suggest the existence of short-range crystalline order in this transformed substance.

Bimodal Energy Relaxation in Quasi-One-Dimensional Compounds with a Commensurate Modulated Ground State

We show that the low temperature (

Complex energy relaxation at very low temperature in linear chain conductors with CDW's or SDW's

T<0.5

Structure property relationship in (TiZrNbCu)1−xNix metallic glasses

K) time dependent non-exponential energy relaxation of quasi-one-dimensional (quasi-1D) compounds strongly differ according to the nature of their modulated ground state. For incommensurate ground states, such as in (TMTSF)

Growing Thin Films of Charge Density Wave System Rb0.3MoO3 by Pulsed Laser Deposition

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