Energy-loss spectra of inelastically scattered X-ray in MgB2

G. STUTZ; G. TIRAO; E. GRANADO; A.F. GARCÍA-FLORES; P.G. PAGLIUSO

Campinas

Congreso; XVII Reunión Anual de Usuarios del LNLS; 2007

LNLS

Soon after the discovery of superconductivity in magnesium diboride [1], much theoretical effort was devoted to studying collective electron excitations in this compound [2, 3]. Those investigations were based on first principles calculations of the frequency- and wave-vector-dependent density response function. Besides the free-electron-like plasmonat » 20 eV, a long-lived plasmon mode at lower energies was predicted by the theoretical models. This novel collective mode was ascribed to strong coherent charge fluctuations betweenparallel Mg and B sheets. By means of high-resolution measurements of inelastic X-ray scattering spectra at low momentum transfers (q < 0.77 a.u.) [4], the predicted energy dispersion and anisotropy of both plasmon modes were experimentally verified. Recently, the low-energy collective excitation was demonstrated to exist not only for small q, but it reappears periodically in higher Brillouin zones [5]. Due to the negligible contribution of multiple-scattering processes,and thus to the negligible distortion of the X-ray energy-loss spectra, and to the enhanced X-ray scattering cross-section at high momentum transfers, inelastic X-ray scattering spectroscopy(IXSS) has become a well-suited technique to investigate electron excitations in the range of intermediate and high momentum-transfers (single-particle excitation domain) [6]. In this work we extend the experimental IXSS studies of electron excitations in MgB2 beyond the plasmon domain.