Determination of the Fermi Surface of Copper by Positron Annihilation

The momentum distribution of annihilation radiation in copper has been determined by unfolding eight accurately measured angular correlations following a new method. The core contribution is found to be anisotropic with a minimum in the [100] directions. The Fermi radii are determined from the half-width of the conduction-electron contribution. Except in the [110] directions, where its radius is at least 5% too large, the shape of the Fermi surface agrees with that obtained from measurements of the de Haas-van Alphen effect. A tentative explanation is offered in terms of a local perturbation of the electron band structure by the positron-electron interaction.