Terahertz Technology: Abstract- High Temperature Terahertz Absorbtion Band in Rare-Earth Gallium

Masaki Adachi1,*, Hiroaki Matsui1,2, Munetoshi Seki1, Hiroyasu Yamahara3, and Hitoshi Tabata1,2,*

1Department of Electrical Engineering and Information Systems, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
2Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
3Institute of Engineering Innovation, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
http://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.085118

*adachi@bioxide.t.u-tokyo.ac.jp; tabata@bioeng.t.u-tokyo.ac.jp

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