OBSERVATION OF CHIRAL SPIN FLUCTUATIONS IN INSULATING PLANAR CUPRATES

A recent theory of Raman scattering in the Hubbard model predicts scattering of A2 symmetry arising from chiral spin fluctuations. In the doped planar cuprates, chiral spin fluctuations have been speculated to play a central role in establishing the normal-state properties. In addition to spin fluctuation scattering in the B1, A1, and B2 symmetries, we report here the direct observation of dynamic chiral spin fluctuations, appearing in the inelastically scattered light of A2 symmetry. In Gd2CuO4, the A2 scattering broadly peaks near 4700 cm-1 (approximately 5J) and extends beyond 8000 cm-1 (1 eV).