Abstract

Raman-scattering studies of the high-T_c superconductor La_2−x(Sr, Ba)_xCuO₄ are briefly reviewed. A detailed analysis of the phonon-mode symmetries is given along with a discussion of the effects expected from the orthorhombic-to-tetragonal phase transition, which is known to occur in these materials. Survey spectra are given for powders, ceramics, and single crystals, and an oxide of Cu is identified as the primary impurity phase. Extensive spectra are given from oriented single crystals of La₂CuO₄ and La_1.85Sr_0.15CuO₄, and several mode assignments are made. Spectra for the high-temperature tetragonal phase and the low-temperature orthorhombic phase are given for each material. The soft phonon associated with the phase transition is seen in La₂CuO₄ as is a broad peak arising from two-magnon scattering. Neither of these features is seen in the Sr-doped sample.

© 1989 Optical Society of America