Anisotropy in the near-edge absorption fine structure ofYBa2Cu3O7−δ

We have observed orientational anisotropy of the near-edge absorption fine structure for the $\mathrm{Cu} 2p$ and $\mathrm{O} 1s$ excitations in single crystals of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ using electron-energy-loss spectroscopy. The $\mathrm{O} 1s$ absorption results suggest that $\mathrm{O}$-derived holes near the Fermi level have $p_{x,y}$ symmetry. The $\mathrm{Cu} 2p$ edge is weakly anisotropic and consistent with some holes having $d_{Z^2}$ symmetry.