Raman Scattering and IR Reflectivity of Oxide Superconductors

Inelastic light scattering, with energy shifts of up to 1 eV, has provided a valuable probe of the spin fluctuation dynamics in the planar cuprates. In particular, Raman studies of La sub 2 CuO sub 4 and Ba sub 2 YCu sub 3 O sub 6, the insulating parent compounds of the high T sub c superconductors, have found well-defined spin-pair excitations of B sub (1g) symmetry at ~ 3000 cm sup (-1). From these data, values of J ~ 1000 cm sup (-1) have been extracted. More recently, we have identified an A sub (1g) symmetry feature in La sub 2 CuO sub 4, in the same energy range as the B sub (1g) light scattering from spin-pair excitations in La sub 2 CuO sub 4 are in quantitative agreement with the moments calculated for the spin-1/2 planar Heisenberg antiferromagnet.