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 Ho3Ga5O12.

DOI: http://dx.doi.org/10.1103/PhysRevB.91.085118

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• Published 20 February 2015
• Received 8 November 2014
• Revised 23 January 2015

©2015 American Physical Society

Abstract-Strong optical reflection of rare-earth garnets in the terahertz regime by reststrahlen bands

Phys. Rev. B 89, 205124 – Published 23 May 2014

Masaki Adachi, Hiroyasu Yamahara, Shunsuke Kawabe, Hiroaki Matsui, and Hitoshi Tabata

The reststrahlen bands of rare-earth garnets were investigated in the terahertz regime. Through this, it was found that the crystal orientation and light polarization directly influence the reststrahlen-related dielectric absorptions of Gd3Ga5O12 (GGG), which is attributed to restriction in the vibrational motion of Gd ions. A theoretical fit to the dielectric absorption revealed that the phonon-polariton frequency in GGG crystals at around 85.5 cm−1 exhibits a narrow spectral width of 100 GHz at room temperature, as estimated using a Lorentz oscillator model. In addition, it was found that the reststrahlen bands can be readily manipulated within a range of 0.7–3.7 THz by changing the chemical composition of the garnet.

DOI: http://dx.doi.org/10.1103/PhysRevB.89.205124

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