Pressure dependence of the thermoelectric power of sodium between 5 and 14 °K

Abstract

The effect of pressure on the thermoelectric power of sodium has been measured between 5 and 14 °K where phonon drag is believed to play a prominent role. A superconducting quantum interference device (SQUID) was used to measure the tiny voltages involved. At 1 and 2 kbar no effect was observable, but at 3 kbar the thermoelectric power was observed to grow smaller in magnitude, but remained negative. The effect of pressure was most noticeable above 11 °K and was monotonically increasing with temperature above that point. The results have been compared with the predictions of a theory of phonon-drag thermoelectric power by Bailyn, which are in rather good qualitative agreement with the data. The results of this experiment therefore support his contention that a detailed understanding of the lattice spectrum, rather than Fermi-surface distortion, is necessary to understand the role of phonon drag in the alkali metals.