Thermopower measurements on bismuth from 9K down to 40 mK

Abstract

Reports the first ultra-low temperature thermopower measurements on bismuth samples of various orientations, including a preliminary study in a small transverse magnetic field. Cooling is provided by a dilution refrigerator, and the thermoelectric voltage is detected using a SQUID null detector. Phonon drag makes a dominant contribution to the thermopower throughout the whole temperature interval investigated. Negative minima are observed on all samples around 0.3 to 0.4K. The position of the positive maxima above 1K seems to correlate with the limiting wavevector of those phonons which can interact with carriers for each particular sample orientation. A large negative phonon drag thermopower of about -10 mu V K^-1 is observed in the bisectrix direction near 4K. The present data and those of J Boxus and J-P Issi indicate that the phonon drag thermopower near 4K is intrinsically negative in the basal plane of bismuth.