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Saturday, February 21, 2015
Abstract- High Temperature Terahertz Absorbtion Band in Rare-Earth Gallium
In addition to the absorption due to known optical phonons, we found a temperature-dependent absorption band at 2 THz in garnet-type Ho3Ga5O12, at temperatures in the range of 450–540 K. The optical and electrical properties reveal that the absorption band at 2 THz is not produced by mechanisms related to soft phonons, rattling phonons, impurities, or charge density waves, but rather to polaron conduction. Our analysis of the scattering rates and optical mobility shows that electron transport via the intermediate polaron is significant in this absorption band. Electrical measurements also support the existence of polarons in Ho3Ga5O12. This paper facilitates a method to investigate charge carrier transport from an optical point of view using terahertz time-domain spectroscopy, which we demonstrate using Ho3Ga5O12.