Density and symmetry of unoccupied electronic states of ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$

The local density and symmetry of unoccupied electronic states at the O and Cu sites in ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ single crystals has been investigated by measuring O 1s and Cu 2p absorption edges. High-energy electron-energy-loss spectroscopy in transmission has been used. There are O 2$p_x$,y states at the Fermi level from the ${\mathrm{CuO}}_2$ planes and O 2$p_z$ states from the BaO and TlO layers. The empty Cu 3d states have predominantly & symmetry. There is an admixture of about & character.