Temperature dependence of the mid-infrared absorptions in undoped cuprate Sr2CuO2Cl2

We have studied temperature dependence of three mid-infrared absorption peaks of Sr2CuO2Cl2, observed in transmission measurement; a lower-energy sharp peak and two higher-energy broad peaks. As temperature increases, the first one shows position redshift and width broadening. We relate the behaviors to Lorenzana and Sawatzky's model [J. Lorenzana, G.A. Sawatzky, Phys. Rev. Lett. 74, 1995, p. 1867] and attribute the peak to the phonon-assisted bimagnon excitation. We examine the temperature dependence of the peak width and suggest magnon scattering mechanism coupled with magnetic disorder in CuO2 plane, in order to explain the anomalous broadening of the width around the Neel temperature. (C) 1998 Elsevier Science B.V. All rights reserved.