The phonon drag component of the thermoelectric power of the alkali metals at low temperatures

Abstract

The theory of phonon drag in the thermoelectric power is developed from an equation derived in a previous paper. It is shown that important in the understanding of the phenomena are the relative probabilities 'α (j q; q + K)that a phonon of wave vector q and polarization j will interact with electrons via a process of umklapp typo K, where K is a reciprocal lattice vector or zero. α(j q, q+K) is the probability relative to all the processes into which the jq phonons can enter, including phonon-phonon collisions and phonon-impurity interactions. It is shown by means of a 'baby spectrum' that the use of α results in the domination of the phonon drag effect by the transverse-like phonon modes, and in the watering down of any ‘bulge’ effect of the Fermi surface. Rough calculations are made that show that one can get qualitative agreement with experiment over at least part of the temperature range from 2 to 20°k. It is shown that with neglect of phonon-phonon and phonon-impurity interactions the phonon drag part S_g of the thermoelectric power is the sum of two terms. a normal (negative) term S_g-, which is exactly what would be calculated if all processes mere non-umklapp processes. plus a term S _g + which is anomalous (positive) in sign and is the effect on the electrons of the Bragg reflections abstracted from the umklapp processes. A simple derivation of the basic equation is given.