Magnetic Raman Scattering in Undoped and Doped Antiferromagnets

摘要

Magnetic Raman scattering of doped and undoped high-T_c (HTc) cuprates is presented in comparison with the conventional antiferromagnet NiO. In both classes of materials the strong magnetic Raman response is caused by a Me-O superexchange mechanism. The difference in the absolute Raman cross-sections of 90 x 10~(-5) sr~(-1) cm~(-1) (YBa_2Cu_3O_(6.3)) and 1.6 x 10~(-5) sr~(-1) cm~(-1) (NiO) is explained by the different strengths of the exchange energies. The magnetic scattering signal of NiO is explainable by the pure Heisenberg model, whereas the zone edge magnons of the HTc cuprates show additional damping due to magnon phonon interaction. On doping, the damping of the zone-edge magnons increases by a factor of 4 more than the decrease of magnon energy. This is characteristic of the interaction of the spin system with the charge carriers. The absolute Raman cross-section is reduced owing to the interruption of antiferromagnetic spin correlations on doping.