Fermi Surface of Lithium by Positron Annihilation

The angular correlation of radiation from positrons annihilating in lithium single crystals has been measured. The crystals were oriented in the [100], [110], and [111] directions, and the measurements yield information closely related to the areas of slices through the Fermi surface normal to these directions. The measurements show that the Fermi surface of lithium is anisotropic, the length of the radius vector $k_{110}$ being about 5% greater than $k_{100}$. The measurements also yield estimates of the energy gap at the boundary of the first Brillouin zone, and the amplitudes of the most important higher-momentum components of the electron wave function.