Excitation wavelength-dependent ultrafast THz emission from surface and bulk of three-dimensional topological insulators

Abstract

Three-dimensional topological insulators possess various interesting properties that are promising for various modern applications, including in the recently emerging fields of ultrafast THz photonics and spintronics. Their gapless spin-momentum-locked topological surface states with the presence of chiral spin structure are relevant for the development of light helicity-sensitive THz emitters and detectors. In this paper, we report femtosecond excitation pulse wavelength and helicity-dependent response of Bi2Te3 and Bi2Se3 for an enhanced broadband THz pulse emission from the surface and bulk states. Specifically, the excitation wavelength has been varied in a large range from near UV to near IR, where it was observed that the photoexcitation at shorter wavelengths enhances the THz emission from both the surface and bulk states but more rapidly from the surface states. These results will be highly relevant for developing chirality-sensitive efficient THz emitters and detectors.