Heat Transport in Bismuth at Liquid-Helium Temperatures

The temperature dependence of the thermal conductivity κ of bismuth has been investigated between 1.3 and 2^∘{}K. In zero magnetic field, this dependence is found to be anisotropic; κ is roughly proportional to T³ for heat flow along the bisectrix, but increases significantly faster than T³ for heat flowing along the trigonal. Application of a small transverse magnetic field ({~}50 Oe) causes the thermal conductivity to drop by several percent at 1.3^∘{}K. This, combined with low-field transverse-magnetoresistance measurements, is cited as evidence for an electronic contribution to the heat current. At higher fields, quantum oscillations in the thermal conductivity are observed, their peak-to-peak amplitude amounting to 7 to 8% of the zero-field conductivity at 1.3^∘{}K. It is suggested that the anisotropic temperature dependence of the thermal conductivity can be understood qualitatively in terms of the electron-phonon interaction for a system which has a very small and highly anisotropic Fermi surface. The electrical resistivity is also measured and found to be proportional to T² between 1 and 4^∘{}K for both directions of current flow; this temperature dependence is unexplained.