Fano-like coupling of collective and particle-hole excitations in Li metal

The dynamic structure factor of Li with 110] and 0.88 a.u. <q< 1.03 a.u., as measured with 1 eV resolution by means of synchrotron radiation based inelastic X-ray scattering spectroscopy (IXSS), exhibits, in the energy loss range between 3 and 12 eV, a fine structure, which appears as a resonance around 4 eV and an antiresonance around 8 eV, when the difference between the experimental -spectra with 110] and 111] is considered. In order to find out the origin of this fine structure we have interpreted recent TLDA (time dependent local density approximation) calculations of the Li- #!ref12!#], which were based on the inversion of the full dielectric matrix, by utilizing a simple two-plasmon-band model. In this way the fine structure can be traced back to a Fano-like coupling of the discrete collective excitations (both the regular plasmon and the so-called zone-boundary collective states (ZBCS's)) and the particle-hole excitation continuum, mediated by the off-diagonal elements of the dielectric matrix, , where (1,1,0). Received: 29 December 1998 / Accepted: 16 March 1998