LINE-SHAPE ANALYSES OF MAGNON RAMAN-SPECTRA OF A PRBA2CU2.7AL0.3O7 SINGLE-CRYSTAL

We present line-shape analyses of magnon Raman spectra in B-1g geometr y of a PrBa2Cu2.7Al0.3O7 crystal for various excitation energies. The description is based on the Heisenberg model of antiferromagnetism. Ou t of resonance, we describe the experimental data by taking into accou nt phonons and a two-magnon excitation using the experimental superexc hange energy J=720 cm(-1) and a damping parameter Gamma=200 cm(-1) of the one-magnon states. After subtraction of the fitted line shapes, we identify three additional spectral features at 730 cm(-1), 1170 cm(-1 ), and 3509 cm(-1). All three show enhanced intensities close to the t wo-magnon resonance at 2.79 eV excitation energy. This strongly sugges ts that these excitations have a magnetic rather than a phononic origi n.