Thermo-emf of metals with open Fermi surfaces at low temperatures

The thermo-emf of metals is examined under conditions when the relaxation is due to small-angle electron-phonon scattering. An equation describing diffusion of electrons along the Fermi surface under the action of a temperature gradient on both the electronic and phonon systems is derived. The role of Umklapp processes and mutual drag of electrons and phonons in the formation of the magnitude and sign of the effect are analyzed in detail. It is shown that in contrast to the case of scattering by impurities phonon-wind induced U processes can make both a positive and negative contribution to the thermo-emf; a criterion is found that determines the sign of the contribution of U processes. Specific calculations of the thermo-emf are performed for models of the Fermi surface close to that of the noble metals, taking into account the special role of transverse phonons, which absorb primarily at the necks of the Fermi surface. The results obtained apparently explain the experimentally observed sign-alternating temperature dependence of the thermo-emf of Ag and Au.

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