Thermoelectric response of a periodic composite medium in the presence of a magnetic field: Angular anisotropy

A calculational method based on Fourier expansion is developed and applied to the study of the strong-field galvanomagnetic thermoelectric properties of a free-electron metal, inside of which is embedded a simple cubic array of identical spheres or cylinders, which have different thermoelectric and conductivity tensors. When the magnetic field is strong enough, the effective galvanomagnetic thermoelectric properties of such composites exhibit very strong variations with the direction of the applied magnetic field with respect to the symmetry axes of the composite microstructure. This is qualitatively similar to the predicted magnetoinduced angular magnetoresistance anisotropy [D. J. Bergman and Y. M. Strelniker, Phys. Rev. B 49, 16256 (1994)] which was verified experimentally [M. Tornow et al., Phys. Rev. Lett. 77, 147 (1996)]. This is a purely classical effect, even though it is qualitatively similar to what is observed in some metallic crystals which have a noncompact Fermi surface. The current results can be useful for studying the possibility of increasing the thermoelectric figure of merit in periodic composites by application of a strong magnetic field. As follows from our very preliminary results, the figure of merit can be increased by application of a strong magnetic field to the composite.