Momentum-Dependent Charge Transfer Excitations in Sr2CuO2Cl2 - Angle Resolved Electron Energy Loss Spectroscopy

Y. Y. Wang; F. C. Zhang; V. P. Dravid; K. K. Ng; M. V. Klein; S. E. Schnatterly; L. L. Miller

doi:10.1103/PhysRevLett.77.1809

paper

Momentum-Dependent Charge Transfer Excitations in Sr2CuO2Cl2 - Angle Resolved Electron Energy Loss Spectroscopy

arXiv:cond-mat/9606064 · doi:10.1103/PhysRevLett.77.1809

Abstract

Electron-hole pair excitations in the insulating cuprates $S r_{2} C u O_{2} C l_{2}$ were investigated by angle-resolved electron energy loss spectroscopy. The optically allowed and optically forbidden transitions were observed to be strongly anisotropic in $C u - O_{2}$ plane. The former show a large energy dispersion $\sim 1.5$ eV along [110], and the latter appear at a higher energy position ( $\sim 4.5$ eV) only along [100], but not along [110]. We interpret these results as transitions involving excitons. A small exciton model is examined to explain both the observed features.

11 pages, RevTex, 3 Postscript figures