Generation and manipulation of chiral terahertz waves in the three-dimensional topological insulator Bi2Te3

Haihui Zhao,Peidi Yang,Yutong Li,Li Wang,Xinhou Chen,Chun Wang,Jungang Miao,Baolong Zhang,Xiaojun Wu,Weisheng Zhao,Chen Ouyang,Deyin Kong,Tianxiao Nie,Hangtian Wang,Gaoshuai Wei

doi:10.1117/1.ap.2.6.066003

Abstract

Arbitrary manipulation of broadband terahertz waves with flexible polarization shaping at the source has great potential in expanding numerous applications, such as imaging, information encryption, and all-optical coherent control of terahertz nonlinear phenomena. Topological insulators featuring unique spin-momentum–locked surface state have already exhibited very promising prospects in terahertz emission, detection, and modulation, which may lay a foundation for future on-chip topological insulator-based terahertz systems. However, polarization-shaped terahertz emitters based on topological insulators with an arbitrarily manipulated temporal evolution of the amplitude and the electric-field vector direction have not yet been explored. We systematically investigated the terahertz radiation from topological insulator Bi2Te3 nanofilms driven by femtosecond laser pulses and successfully realized the generation of efficient chiral terahertz waves with controllable chirality, ellipticity, and principal axis. The convenient engineering of the chiral terahertz waves was interpreted by a photogalvanic effect (PGE)-induced photocurrent, while the linearly polarized terahertz waves originated from linear PGE-induced shift currents. Our work not only provides further understanding of femtosecond coherent control of ultrafast spin currents but also describes an effective way to generate spin-polarized terahertz waves at the source.

Highlights

Spin-polarized terahertz waves with twisted electric- and magnetic-field directions and temporal evolution of the amplitudes have been widely utilized for non-thermal and selective excitation of electron spins, resulting in the discovery of the spin-galvanic effect,[1] the manipulation of terahertz nonlinear phenomena,[2] and optical spin injection in novel materials.[3,4,5] Recently, Mashkovich et al.[6] found that linearly polarized terahertz waves can nonlinearly excite gigahertz spin waves in antiferromagnetic FeBO3 via terahertz field-induced inverse Cotton–Mouton effect
The topological insulator samples were grown by molecular beam epitaxy (MBE), and their lattice structures and the characterizations
We systematically studied terahertz emission from topological insulator Bi2Te3 nanofilms driven by femtosecond laser oscillator pulses

Summary

Introduction

Excitation of electron spins, resulting in the discovery of the spin-galvanic effect,[1] the manipulation of terahertz nonlinear phenomena,[2] and optical spin injection in novel materials.[3,4,5] Recently, Mashkovich et al.[6] found that linearly polarized terahertz waves can nonlinearly excite gigahertz spin waves in antiferromagnetic FeBO3 via terahertz field-induced inverse Cotton–Mouton effect. Based on the radiated terahertz characteristics, which originated from the helicitydependent photocurrent component featuring the spin selectivity in the surface state [Fig. 1(b)] and other components in the bulk state30 [Fig. 1(c)], we provide a phenomenological PGE-based interpretation for the polarization tunable terahertz radiation mechanism. Such polarization-shaped topological insulatorbased terahertz source can be used for terahertz circular dichroism spectroscopy, terahertz secure wireless communication, and electron spin correlated coherent excitation and manipulation investigations

Experimental Results

Mechanism of Linearly Polarized Terahertz Emission

Chiral Terahertz Wave Emission and Manipulation

Conclusion