Abstract-Infrared/terahertz spectra of the photogalvanic effect in (Bi,Sb)Te based three-dimensional topological insulators

H. Plank, J. Pernul, S. Gebert, S. N. Danilov, J. König-Otto, S. Winnerl, M. Lanius, J. Kampmeier, G. Mussler, I. Aguilera, D. Grützmacher, and S. D. Ganichev

https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.024202

We report on the systematic study of infrared/terahertz spectra of photocurrents in (Bi,Sb)Te based three-dimensional topological insulators. We demonstrate that in a wide range of frequencies, ranging from fractions up to tens of terahertz, the photocurrent is caused by the linear photogalvanic effect (LPGE) excited in the surface states. The photocurrent spectra reveal that at low frequencies the LPGE emerges due to free carrier Drude-like absorption. The spectra allow us to determine the room temperature carrier mobilities in the surface states despite the presence of thermally activated residual impurities in the material bulk. In a number of samples we observed an enhancement of the linear photogalvanic effect at frequencies between 30 and 60 THz, which is attributed to the excitation of electrons from helical surface to bulk conduction band states. Under this condition and applying oblique incidence we also observed the circular photogalvanic effect driven by the radiation helicity.

• 
• 
• 
• 

Abstract-Effect of optical pumping on the dielectric properties of 0.6CaTiO3-0.4NdAlO3 ceramics in the terahertz range

Dan Li, Chunya Luo, Yebin Xu, Jing Zhang, Liang Wu, Huaixing Wang, Songjie Shi, Furi Ling, and Jianquan Yao

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-1-1&origin=search

The dielectric properties of 0.6CaTiO3-0.4NdAlO3$0.6{\mathrm{CaTiO}}_3\text{-}0.4{\mathrm{NdAlO}}_3$ ceramics under external optical fields were investigated by terahertz time-domain spectroscopy in a frequency range of 0.2 THz to 1 THz at room temperature. It could be found that the variation of the real part of complex permittivity is approximately 0.31 in the frequency range of 0.2 THz to 1 THz. However the imaginary part of the dielectric constant does not change appreciably with the external optical field. The micromechanism of these results was attributed to the built-in electric field caused by the excited free carriers in the ceramics.

© 2017 Optical Society of America