Thermal properties of (formula presented) near the charge-density-wave transition

We report the investigations of specific heat, thermal conductivity, as well as thermoelectric power on the charge-density-wave (CDW) compound (formula presented) as a function of temperature. All thermal measurements consistently exhibit anomalous features around the CDW transition temperature (formula presented) Although the observations can be associated with the CDW formation, the measured anomalies are significantly large, in contrast to those in weak-coupled CDW materials. A quantitative analysis for the specific-heat data near the fluctuation region yields a critical exponent (formula presented) much larger than the predicted value (formula presented) in the extended mean-field theory assuming three-dimensional fluctuations. We also obtained a ratio (formula presented) a factor of 6 larger than the BCS value 1.43 in the weak-coupling limit, indicating a strong coupling of this phase transition. Besides, the observed giant excess specific heat (formula presented) and thermal conductivity (formula presented) at (formula presented) further support this strong-coupling scenario. These large enhancements in (formula presented) and κ are attributed to the results of substantially thermal excitation and heat carried by the soft phonons at the transition. In addition, a rapid change in the sign of thermoelectric power at (formula presented) was observed, which provides a better understanding of the evolution of electronic band structure of the system below and above the CDW formation.