DYNAMIC STRUCTURE OF ELECTRONS IN AL METAL STUDIED BY INELASTIC X-RAY-SCATTERING

The dynamic structure factor S (q, omega) of electrons in single-crystal Al metal was measured with 1.4-eV resolution by means of inelastic x-ray-scattering spectroscopy for q parallel to [100] and for q parallel to [110] with 0. 37 < q < 2.06 a.u. using synchrotron radiation from DORIS storage ring. The overall shape of the experimental dynamic structure factors is in agreement with jellium calculations which extend the random-phase approximation by taking into account both local-field corrections and the influence of the momentum-dependent lifetime of the quasiparticles. Besides some q-orientation-dependent fine structure, the S (q, omega) spectra for q > 1.1 a.u. exhibit a q-orientation-independent double-peak or one-peak-one-shoulder fine structure. Whereas the q-orientation-dependent fine structure can be attributed to ion-lattice-induced indentations in the electron-hole excitation continuum due to Bragg reflections, the origin of the q-orientation-independent fine structure could not be clarified definitively. The most probable explanation of this fine structure which is based on semiquantitative agreement with model calculations is the shifting down of unoccupied d-like bands due to the lack of d core-state orthogonalization. Alternative interpretations on the basis of special features of the short-range electron correlations (lifetime effects, multiple-pair excitation, plasmaron ground state) have either failed or have been left on the level of qualitative and somewhat speculative arguments.