Electron Momentum Distribution in Liquid and Solid Rubidium and Cesium as Determined by Positron Annihilation

Abstract

The momentum distributions of photons from positrons annihilating in liquid and solid rubidium and cesium and in solid krypton and xenon have been measured. The krypton and xenon data are used to remove the core contributions in rubidium and cesium, respectively. Analysis of the resultant conduction-electron momentum distribution shows that (a) indications of higher-momentum components due to scattering into the second zone appear to be predominately a result of core annihilations and largely disappear when the core contribution is removed, and (b) the free-electron model is reasonably accurate for the liquid as well as the solid metals. The core contributions in rubidium and cesium closely approximate a Gaussian distribution. There is little or no change in the ratio of the broad-to-narrow components upon melting.