Study of the Infrared Properties of (La_1-xSr_x)₂CuO₄

Abstract

Reflectivity and transmission spectra of (La 1- x Sr x ) 2 CuO 4 were measured in the spectral range of 20-4800 cm -1 . The intensity of the absorption peak around 255 cm -1 became twice with lowering temperature from 298 to 19 K accompanying weak softening, while the Cu-O asymmetric stretching mode at 510 cm -1 was almost unchanged both in its energy and intensity. The origin of the soft-phonon mode is discussed.