Electron momentum distribution in Al and Al 0.97 Li 0.03

High resolution Compton profiles from single crystals of Al and Al 0.97 Li 0.03 have been measured along the principal crystallographic directions [100], [110], and [111] using monochromatic synchrotron radiation at two different photon energies. The spectra were recorded by a scanning spectrometer with a momentum resolution of 0.08 a.u. for 29 keV and 0.16 a.u. for 58 keV radiation. Corresponding, highly accurate computations on Al 0.97 L 0. 03 and Al have been carried out within the framework of the selfconsistent KKR-CPA scheme, including the limiting case of a single impurity. A good overall accord is found between theory and experiment with respect to the anisotropies as well as the amplitudes and fine structure in the first and second derivatives of the directional profiles. The Fermi break is found to be the sharpest along the [111] direction in Al and the alloy. The [110] direction shows an anomalously large discrepancy between theory and experiment near the Fermi momentum, suggesting that the present LDA based crystal potential does not reproduce fine details of the electron rings of the 3rd band in Al accurately. The effects of alloying are analyzed by taking differences between profiles of Al and Al 0.97 Li 0. 03 , and it is shown that these results can be explained to a first approximation within a free electron model by the depletion of 0.06 electrons/atom from the Fermi surface of Al.