Magnetic Raman scattering of insulating cuprates

We study the B-1g and Alg Raman profiles of M2CuO4 (with M = La, Pr, Nd, Sm , Gd), Bi2Sr2Ca0.5Y0.5Cu2O8 + y, YBa2Cu3O6.2, and PrBa2Cu2.7Al0.3O7 insulat ing cuprates within the Loudon-Fleury theory, in the framework of an extend ed Hubbard model for moderate on-site Coulomb interaction U. We calculate t he nonresonant contribution to these Raman profiles by using exact diagonal ization techniques and analyze two types of contributing mechanisms to the line shapes: four-spin cyclic exchange and spin-phonon interactions. Althou gh these interactions contribute to different parts of the spectra, togethe r, they account for the enhanced linewidth and asymmetry of the B-1g mode, as well as the non-negligible intensity of the A(1g) Raman line observed in these materials. [S0163-1829(99)00901-7].