Plasmons and interband transitions in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$Ca${\mathrm{Cu}}_2$${\mathrm{O}}_8$

Electron energy-loss spectroscopy has been used to investigate the electronic structure of single-crystalline ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$Ca${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$. The dielectric function was derived in the energy range of 0.2-48 eV. Information on interband transitions and low-lying core levels is obtained. The charge-carrier plasmon shows a quadratic dispersion in momentum transfer. From the dispersion constant the Fermi velocity of the charge carriers could be derived.