FERMI-SURFACE SIGNATURES IN THE COMPTON PROFILE OF BE

We report high-resolution Compton profiles of two single crystals of B e with surface normals oriented along the [0001] and [11 (2) over bar 0] directions. The results are compared and contrasted with correspond ing, highly accurate all-electron computations based on the band theor y framework within the local-density approximation (LDA). A reasonable overall level of agreement is seen between theory and experiment with respect to the shapes of the Compton profiles, as well as the Fermi-s urface-induced finer structure in the first and second spectral deriva tives. However, the measured profiles are lower than theory at low mom enta, clearly displaying broadened Fermi surface features compared wit h the theoretical predictions, and point to the importance of electron correlation effects beyond the LDA for a proper description of the mo mentum density. The aforementioned similarities and differences betwee n theory and experiment in Be are rather like the situation that has b een observed in recent high-resolution Compton studies of other materi als. (C) 1997 Elsevier Science Ltd. All rights reserved.