Effect of exchange splitting on the low-energy optical absorption in heavy rare-earth metals

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Abstract
A detailed experimental investigation of the temperature dependence of the resonance anomaly on the dispersion curves of optical conductivity has been carried out on single crystals of Gd, Tb and Dy. This dependence is related to electron transitions between valence states split by the exchange field of the 4f shell. Over the entire temperature range of existence of the optical conductivity peak, its position on the energy scale is stable. Magnetic phase transitions of the ferromagnet-spiral type have not brought about any noticeable changes of peak parameters. The theoretical interpretation of the properties of the observed anomaly is based on direct calculations of the electronic structure and interband density of states for ferromagnetic and spiral configurations of magnetic moments. It is shown that, in the electronic spectrum of rare-earth metals, there is a region that remains relatively stable in the course of changes of the magnetic configuration and is responsible for the stability of the energy localization of the investigated peak.