Abstract:
We have studied the electron–phonon interaction (EPI) in multiferroic $\rm{PrFe_3(BO_3)_4}$ applying reflection methods in far-infrared (terahertz) spectral range and theoretical simulations. A specific feature of $\rm{PrF_3(BO_3)_4}$ is that the 4f-electron excitation of the $\rm{Pr^{3+}}$ ion falls into a range between the longitudinal (LO) and transverse (TO) phonon mode frequencies. Simultaneously, inversion of the electronic oscillator occurs: its LO frequency becomes smaller than the TO frequency. With lowering temperature, a coupled electron–phonon mode emerges, and a new effect is observed: the reststrahlen band corresponding to a nondegenerate phonon mode splits. Yet another effect caused by the EPI is the appearance of a gap in the spectrum of electronic excitations of a stoichiometric rare-earth easy-axis antiferromagnet placed into an arbitrarily weak external magnetic field directed along the easy magnetization axis.
Keywords:inverted electronic oscillator, electron–phonon interaction, coupled electron–phonon mode, bifurcations in a magnetic field, terahertz spectroscopy.
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