Diffraction of correlated electron pairs from crystal surfaces

The spectra of the internal energy distribution of correlated electron pair s, ejected from W(0 0 1), Fe(1 1 0) and Cu(0 0 1) following the impact of a low-energy electron, show characteristic structure that can be associated with the diffraction of two-electron quasi-particles from the periodic surf ace potential. In this combined theoretical and experimental work we show t hat the positions of these features in momentum space are determined by the amount of change of the center-of-mass wave vector of the pairs with respe ct to the surface reciprocal lattice vector. This corresponds to a two-part icle Bragg diffraction. The relative intensities of the peaks and the shape s of the peaks depend mainly on the internal correlation of the electron pa ir, i.e. on the strength of the electronic interaction. (C) 2000 Elsevier S cience B.V. All rights reserved.