Observation of a new anomaly in the low-temperature thermoelectric power of graphite: Interpretation by a phonon-drag effect acting on theH-point minority holes

We present the results of new measurements of the basal-plane thermoelectric power $S$ of highly oriented pyrolytic graphite between 1.3 and 300 K. In addition to the well-known large negative dip near 40 K, the curve of $S\left(T\right)\mathrm{}$ reveals the presence of a second anomaly in the region below about 10 K. We show that this extra anomaly can be explained in terms of a phonon-drag effect acting on the $H$-point hole minority carriers. Such an interpretation is consistent with other experimental data.