Anisotropic exchange integrals in the two-leg spin ladder LaCuO2.5

The magnetic excitation in a two-leg S = 1/2 antiferromagnetic spin ladder is strongly dependent on the anisotropy in exchange integrals. The exchange integrals along the leg J(parallel to) and the rung J(perpendicular to) were obtained separately by polarized micro-Raman scattering in single domains of polycrystalline LaCuO2.5. The exchange integrals are J(parallel to) = 1012 cm(-1) and J(perpendicular to) = 957 cm(-1) after correcting the quantum spin effects. The anisotropy is found to be small as J(perpendicular to)/J(parallel to) = 0.95. [S0163-1829(99)50734-0].