Momentum-Dependent Charge Transfer Excitations inSr2CuO2Cl2Angle-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
1996 Physical Review Letters  
Electron-hole pair excitations in the insulating cuprates $Sr_2CuO_2Cl_2$ were investigated by angle-resolved electron energy loss spectroscopy. The optically allowed and optically forbidden transitions were observed to be strongly anisotropic in $Cu-O_2$ 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
more » ... olving excitons. A small exciton model is examined to explain both the observed features.
doi:10.1103/physrevlett.77.1809 pmid:10063177 fatcat:pkukawv3pvegpbo6yxcbhp7ws4