K. Biljaković

Thermal hysteresis in thermopower of the charge-density-wave system (NbSe4)10I3

Measurements of the thermopower in the charge density wave compound (NbSe4)10I3 show a large hysteresis between the cooling and heating cycles below and above the Peierls transition temperature. The magnitude of the observed hysteresis depends on the lowest temperature reached in the cooling regime. This effect is attributed to the interaction between charge density wave deformations and a quasi-periodic structure of lattice defects.

Low-energy excitations in C.D.W. compounds investigated by low-temperature specific heat

We have measured the specific heat on several charge density wave compounds (NbSe 3 , TaS 3 , KCP, (TaSe 4 ) 2 I, K 0.3 MoO 3 ) at very low temperatures (T≤1 K). All these quasi one-dimensional compounds exhibit an excess heat capacity contribution C p following a T ν power law (ν

Structural modification and heat capacity of ZrTe5

Abstract Orthorhombic and monoclinic polytypes of ZrTe 5 are examined by X-ray camera techniques at room temperature. Long period modulation of the former was determined. Lattice parameters of the monoclinic polytype are given. Two peaks are observed in the heat capacity of the orthorhombic crystal. One is assigned to a phase transition in the monoclinic inclusion. Another peak at 135K appears as the result of thermal excitation of electrons in a semimetallic energy band.

Manifestation of disordered CDWs in specific heat measurements

Abstract We discuss heat capacity properties of several commonly investigated CDW systems, the members of the transition metal chalcogenide family : NbSe 3 , TaS 3 and (TaSe 4 2 I. Several observed effects can be ascribed to the disorder of CDWs: hysteresis below the Peierls transition, a contribution to the specific heat from low-energy excitations of metastable CDW states (C p ≈ T α , α ⩽ 1) as well as the failure of ergodicity via non-exponential thermal relaxation below some temperature T K . We show that the similarity in the thermal properties with other glassy systems may also be established at very low temperatures. The phason contribution to the specific heat anomaly observed in (TaSe 4 ) 2 I at 1.75 K is also discussed.

Glassy-like thermodynamical properties of (TMTSF)2PF6

Abstract We report on specific heat measurements of (TMTSF) 2 PF 6 between 0.1 and 25 K. In addition to the small anomaly at the SDW transition temperature, this SDW compound exhibits all characteristics of the low temperature thermodynamical properties of CDW systems. These typical features are additional excitations to regular phonons contributing to the specific heat below 0.5 K which are reminiscent of low-energy excitations in glasses and the enthalpy relaxation exhibiting aging effects such as in other disordered systems. Finally, the role of the isothermal annealing and the kinetics of measurements on the specific heat anomaly in the range 2.5–5 K are indicative of a glass transition in the general frame of freezing of supercooled liquids.

The dynamics around the glass transition in the spin density wave ground state of TMTSF2PF6

We present experimental observations of the dielectric and energy relaxations in the spin density wave state of TMTSF2PF6. These measurements reveal two distinct dynamical regimes. The dielectric relaxation shows a critical slowing down towards a static glass transition around 2 K. Below this temperature very slow energy relaxation processes appear, which exhibit breaking of ergodicity associated with aging effects. These results are analysed within the framework of glass-forming systems.

Thermal properties of (NbSe4)3I

Abstract We report measurements of thermal conductivity and thermal capacity of halogenated niobium tetraselenide (NbSe 4 ) 3 I. The structural phase transition at 274K is clearly marked in both measurements. Thermal conductivity shows significant differences between heating and cooling cycles which begin around 200K.

Glassy Behaviour and Metastability in the Charge or Spin Density Wave State

A charge or spin density wave (DW) in its ground state, where the phase is pinned to the underlying ionic lattice by impurities, crystalline defects or commensurations, is characterized by a “glassy” behaviour for numerous physical properties in relation with the existence of many metastable sates. DW systems show anomalously slow relaxations in very different energy-time windows [1] and they represent a special group of glasses with some very unique features among the found universalities.

Anisotropy of the thermal conductivity in blue bronze

Abstract We have measured the thermal conductivity of K 0.3 MoO 3 (blue bronze) in the chain direction and in both perpendicular directions from 80 to 300 K. As expected, it shows an anisotropic behaviour in lattice contribution as well as in free carrier contribution. These results are in favor to our previous explanation that there are residual anomalies in thermal conductivity resulting from the contribution of low-frequency phasons of rather large velocities.

Heat Capacity Measurements on TaS3

Abstract We have measured the heat capacity of TaS3 in the temperature range 60-180K with a resolution better than 2% in order to Investigate hysteresis effects around 100K. We observe hysteresis in heat capacity between 100K and 130K which corresponds to the resistivity hysteresis and to some anomalies in non linear properties associated with the motion of the. CDW.