Charge-transfer spectrum and its temperature dependence inLa2CuO4

The reflectivity and its temperature dependence in the neighborhood of the charge-transfer band is reported for carrier-free ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$. There is a sharp peak in the imaginary part of the dielectric function for light polarized parallel to the ${\mathrm{CuO}}_2$ layers. It is shown that the line shape as well as its temperature dependence is consistent with short-range electron-hole interaction in the final state of the charge-transfer excitation broadened by moderate coupling to optical phonons.