Thermal properties of Lu 5 Ir 4 Si 10 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 ͑CDW͒ compound Lu 5 Ir 4 Si 10 as a function of temperature. All thermal measurements consistently exhibit anomalous features around the CDW transition temperature T o ϳ80 K. 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 ␣ϳ2, much larger than the predicted value ␣ϭ0.5 in the extended mean-field theory assuming three-dimensional fluctuations. We also obtained a ratio ␥*/␥ϭ8.4, 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 ⌬C p /C p ϳ26% and thermal conductivity ⌬/ϳ15% at T o further support this strong-coupling scenario. These large enhancements in C p and 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 T o was observed, which provides a better understanding of the evolution of electronic band structure of the system below and above the CDW formation