Thermal conductivity studies near a smectic-A - hexatic-B transition in one liquid-crystal compound.

High-resolution thermal conductivity and heat capacity measurements have been carried out in the vicinity of the smectic-A-hexatic- B transition of n-hexl-4'-n-pentyloxybiphenyl-4-carboxylate (650BC). Both thermal conductivity and heat capacity display divergent behavior near this transition. A power law fitting with background contribution to the thermal conductivity data leads to a dynamic critical exponent a = 0.51+-0.04 and a ratio of critical amplitude Lamda+/Lamda- = 0.93+-0.10. In light of our measured critical exponents for thermal conductivity and heat capacity, we will discuss their relation based on a dynamic scaling law for a helium-like system. Furthermore, the thermal diffusivity which is the ratio of the thermal conductivity to the heat capacity shows a pronounced drop near the transition. This suggests the critical slowing of the thermal fluctuations.