Line-shape analyses of magnon Raman spectra of a Pr${\mathrm{Ba}}_2$${\mathrm{Cu}}_{2.7}$${\mathrm{Al}}_{0.3}$${\mathrm{O}}_7$ single crystal

We present line-shape analyses of magnon Raman spectra in $B_{1g}$ geometry of a Pr${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_{2.7}$ ${\mathrm{Al}}_{0.3}$ ${\mathrm{O}}_7$ crystal for various excitation energies. The description is based on the Heisenberg model of antiferromagnetism. Out of resonance, we describe the experimental data by taking into account phonons and a two-magnon excitation using the experimental superexchange energy $J=720\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and a damping parameter $\Gamma =200\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ of the one-magnon states. After subtraction of the fitted line shapes, we identify three additional spectral features at 730 ${\mathrm{cm}}^{-1\mathrm{}}$, 1170 ${\mathrm{cm}}^{-1\mathrm{}}$, and 3500 ${\mathrm{cm}}^{-1\mathrm{}}$. All three show enhanced intensities close to the two-magnon resonance at 2.79 eV excitation energy. This strongly suggests that these excitations have a magnetic rather than a phononic origin.