Magnetothermal emf of phonon drag in uncompensated metals with open Fermi surfaces at low temperatures

The thermo-emf of the phonon drag of a metal in a strong magnetic field under conditions when the dominant relaxation mechanism is small-angle electron–phonon scattering is studied. It is pointed out that the role of Umklapp processes in the thermo-emf differs fundamentally from their role in electrical conductivity: here the escape of electrons to infinity, determined by the U processes, in p space is not required. As a result, the significant anisotropy of the thermo-emf is not linked in the general case with U processes. It is shown, however, that in noble metals, in which the “phonon wind” affects primarily the electrons from small necks in the Fermi surface, the anisotropy of the thermo-emf Sxx (x⊥H) and of the electrical conductivity are similar to some extent, though they have a different physical origin. The effect of the crystallographic symmetry on the dependence of the thermo-emf on the strong magnetic field is studied. It is shown that there is a significant difference in the behavior of the adiabatic thermo-emf measured and Sxx. An explanation is proposed for a number of experimentally observed features of the thermo-emf.

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