One-magnon Raman scattering in La2CuO4: The origin of the field-induced mode

We investigate the one-magnon Raman scattering in the layered antiferromagnetic La2CuO4 compound. We find that the Raman signal is composed by two one-magnon peaks: one in the B1g channel, corresponding to the Dzyaloshinskii-Moryia mode, and another in the B3g channel, corresponding to the XY mode. Furthermore, we show that a peak corresponding to the XY mode can be induced in the planar (RR) geometry when a magnetic field is applied along the easy axis for the sublattice magnetization. The appearance of such a field-induced mode signals the existence of a magnetic state above the Néel temperature TN, where the direction of the weak-ferromagnetic moment lies within the CuO2 planes. © 2005 The American Physical Society.