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تسجيل مستخدم جديدElectric-dipole active two-magnon excitation in {textit{ab}} spiral spin phase of a ferroelectric magnet Gd$_{textbf{0.7}}$Tb$_{textbf{0.3}}$MnO$_{textbf 3}$
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A broad continuum-like spin excitation (1--10 meV) with a peak structure around 2.4 meV has been observed in the ferroelectric $ab$ spiral spin phase of Gd$_{0.7}$Tb$_{0.3}$MnO$_3$ by using terahertz (THz) time-domain spectroscopy. Based on a complete set of light-polarization measurements, we identify the spin excitation active for the light $E$ vector only along the a-axis, which grows in intensity with lowering temperature even from above the magnetic ordering temperature but disappears upon the transition to the $A$-type antiferromagnetic phase. Such an electric-dipole active spin excitation as observed at THz frequencies can be ascribed to the two-magnon excitation in terms of the unique polarization selection rule in a variety of the magnetically ordered phases.
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