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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 , and the latter appear at a higher energy position ($\sim 4.5$eV) only along , but not along . We interpret these results as transitions involving excitons. Adoi:10.1103/physrevlett.77.1809 pmid:10063177 fatcat:pkukawv3pvegpbo6yxcbhp7ws4