Optical constants, heat capacity and the fermi surface

Thermal and optical effective masses are defined and expressions for them obtained for metals with arbitrary Fermi surfaces. The ratio of these two effective masses is shown to depend on the shape of the Fermi surface. It follows from experimental values of the optical constants and the electronic heat capacity that the Fermi surface is not spherical in Cu, Ag and Au and that it contacts the surface of the first Brillouin zone to an appreciable degree in Cu and Ag. Similar evidence indicates a non-spherical Fermi surface in Li, Na and K. A simplification of the theory of the optical constants of metals is given which fits the experimental data for Na, K, Rb and Cs satisfactorily. Values of the plasma frequencies and widths of the plasma resonances of the alkali metals are calculated.