We have studied the electron—phonon interaction (EPI) in multiferroic ${\text PrFe}_3({\text BO}_3){}_4$ using far-infrared (terahertz) reflection and theoretical simulation. A specific feature of ${\text PrFe}_3({\text BO}_3){}_4$ is that the 4f electronic excitation of the ${\text Pr}^{\,3+}$ ion falls into a range between the longitudinal (LO) and transverse (TO) phonon frequencies. Inversion of the electronic oscillator occurs: its LO frequency becomes smaller than the TO frequency. As temperature diminishes, a coupled electron—phonon mode emerges, and a new effect is observed: the reststrahlen band corresponding to a nondegenerate phonon mode splits. Another effect caused by the EPI is the existence 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 magnetic field, terahertz spectroscopy PACS: 63.20.kd, 71.70.−d, 75.50.Ee, 75.85.+t, 78.20.Bh, 78.30.−j (all) DOI: 10.3367/UFNe.2018.06.038413 URL: https://ufn.ru/en/articles/2019/3/f/ 000469214700006 2-s2.0-85069543197 2019PhyU...62..275P Citation: Popova M N, Boldyrev K N "New effects of the electron—phonon interaction in dielectrics" Phys. Usp. 62 275–281 (2019) BibTexBibNote ® (generic)BibNote ® (RIS)MedlineRefWorks Received: 12th, August 2018, accepted: 20th, June 2018 Оригинал: Попова М Н, Болдырев К Н «Новые эффекты электрон-фононного взаимодействия в диэлектриках (к 50-летию Института спектроскопии РАН)» УФН 189 292–298 (2019); DOI: 10.3367/UFNr.2018.06.038413