SIZE EFFECT IN ELECTRICAL CONDUCTION OF BISMUTH

The dependence of the electrical conductivity at 4·2°K upon sample thickness has been studied for a number of pure single-crystal bismuth samples. The results suggest that two distinct size effects occur, one at sample thicknesses of about 2·5 mm and the other at thicknesses of about 1 mm and less. It is suggested that the former is due to boundary scattering of phonons leading to the elimination of an enhancement of the sample conductivities arising from phonon drag, while the latter is a conventional electron mean-free-path size effect. On the basis of this hypothesis, values are found for electron and phonon mean free paths in the samples.