Thermal properties ofLu5Ir4Si10near the charge-density-wave transition

Abstract

We report the investigations of specific heat, thermal conductivity, as well as thermoelectric power on the charge-density-wave (CDW) compound ${\mathrm{Lu}}_5{\mathrm{Ir}}_4{\mathrm{Si}}_{10}$ as a function of temperature. All thermal measurements consistently exhibit anomalous features around the CDW transition temperature $T_o\sim 80\mathrm{K}.$ 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 $\alpha \sim 2,$ much larger than the predicted value $\alpha =0.5\mathrm{}$ in the extended mean-field theory assuming three-dimensional fluctuations. We also obtained a ratio ${\gamma }^{*}/\gamma =8.4,$ 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 $\Delta C_p{/C}_p\sim 26\%$ and thermal conductivity $\Delta \kappa /\kappa \sim 15\%$ at $T_o$ further support this strong-coupling scenario. These large enhancements in $C_p$ 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 $T_o$ was observed, which provides a better understanding of the evolution of electronic band structure of the system below and above the CDW formation.