Thermal conductivity and thermopower of graphite at very low temperatures

Measurements of the in-plane thermal conductivity and thermopower of graphite have been performed from 70 mK to 8 K. The thermal conductivity exhibits a crossover from a $T^n$ (n>2) dependence above 1 K to a $T^{1.14\pm 0.02}$ law at lower temperatures, behavior attributed to a combination of increasing carrier conduction and a lattice component varying slower than $T^2$ from 1 K down to about 0.3 K. The thermoelectric power is negative throughout the range; below 2 K, it is a linear function of temperature, the magnitude of the slope being proportional to the degree of structural imperfection of the samples.