Helicity‐dependent THz emission realized in a novel topological material

Terahertz electromagnetic wave, whose frequency located in the domain between the microwave and the infrared, is within an electromagnetic spectrum that needs to be further studied and developed. It plays an important role in frontier scientific research, national security and information technology. At present, the key to the development of this technology lies in the acquisition of efficient terahertz radiation sources, highly sensitive detectors and various functional devices. Among them, the development of efficient terahertz radiation source is particularly important. The helicity-dependent ultra-fast current generated by circularly polarized photons in topological materials is the key to the improvement of quantum communication, on-chip communication processing and information storage. On the one hand, the spin current generated in the picosecond timescale makes ultra-fast optical manipulation possible. It is well known that efficient data storage and processing can be achieved by means of spin degrees of freedom. However, this requires the generation and control of spin currents in transient times for ultra-fast operations, especially in untapped terahertz frequencies. The unique spin current in topological materials allows ultra-fast operation in circularly polarized light without an external field. Additionally, the spin photocurrent induced electromagnetic wave in the terahertz frequency domain has been proved to be a highly efficient form of spin terahertz radiation. It is worth mentioning that in the past, the generation and manipulation of spin terahertz pulses mainly depended on the complex pulse shaping or the two-color manipulation of the incident laser, while the radiation source itself had no unique manipulation characteristics. Therefore, it is very important to develop new topological materials with peculiar spin - momentum locking properties.

Figure 1 (a) Schematic of the THz emission configuration. Polar plots of terahertz waveforms (0~4.65 ps) as a function of α at (b) θ = -45º and (c) +45º, respectively, for φ = 0º. The colors represent the amplitude of the terahertz emissions.

The research group of Prof. Jiang from National University of Defense Technology proposes a novel approach that realizes helicity-dependent terahertz emission in a new topological material. Started by exploring how to regulate the generated terahertz polarization properties arbitrarily, a circular polarization terahertz radiation, after the stimulation from femtosecond laser, was generated successfully in nodal-line semimetal candidate Mg3Bi2 thin film through the electronic spin characteristics. It is found that the terahertz radiation mainly comes from the spin dependent photocurrent caused by the circular photovoltaic effect and the spin independent photocurrent caused by the linear photovoltaic effect. In this work, the polarization and intensity of terahertz radiation can be manipulated by the polarity and power of the incident laser, as well as the azimuth of the sample. This work will stimulate the exploration of novel topological materials and provide new opportunities for the development of ultra-fast optoelectronic technologies in topological systems. The article is entitled “Helicity–dependent THz emission induced by ultrafast spin photocurrent in nodal-line semimetal candidate Mg3Bi2” and published in Opto-Electronic Advances Issue 12 2020.

About The Group

Jiang Tian is the deputy director of the Faculty of cross-discipline of the National University of Defense Technology. He was selected into the Youth Talent Support Project of China Association for Science and Technology, outstanding youth of Hunan Province, and won second Prize of National Science and Technology Progress award (ranked 2nd). He has been engaged in the research of photoelectric technology, ultra-fast spectral detection (femtosecond transient spectrum and terahertz transient spectrum), microwave photons, infrared terahertz functional devices and ultra-fast spintronics. He has 30 SCI articles published as the first author or corresponding author, among which 3 papers were listed in the top 1% of ESI and 1 article was listed in the top 0.1% ESI hot spot.

Representative papers:

1. Ke Wei†, Yizhen Sui† , Zhongjie Xu†, Yan Kang , Jie You , Yuxiang Tang , Han Li , Yating Ma , Hao Ouyang , Xin Zheng , Xiangai Cheng, Tian Jiang*. Acoustic phonon recycling for photocarrier generation in Graphene-WS2 heterostructures,  Nat Commun 11(1), 3876 (2020).
2. Yuze Hu†, Tian Jiang†*, Junhu Zhou†, Han Li, Yizhen Sui, Hao Hao, Jie You, Xin Zheng, Zhongjie Xu, Xiangai Cheng. Ultrafast THz Transmission and Slow Light Switching with Photoactive WSe2 -hybrid Metadevice, Nano Energy 68 :104280(2020).
3. Tong, M. Y. †; Hu, Y. Z†.; Wang, Z. Y.; Zhou, T.; Xie, X. N.; Cheng, X. A.; Jiang, T.*. Enhanced Terahertz Radiation by Efficient Spin-to-Charge Conversion in Rashba-Mediated Dirac Surface States. Nano Lett (2020). 
4. Yuze Hu†, Jie You†, Mingyu Tong†, Hao Sun, Xin Zheng, Zhongjie Xu, Xiangai Cheng and Tian Jiang*. Pump-Color Selective Control of Ultrafast All-Optical Switching Dynamics in Metaphotonic Devices. Advance Science 7(14), 2000799 (2020).

5. Yuze Hu†, Tian Jiang†*, Hao Sun†, Mingyu Tong, Jie You, Xin Zheng, Zhongjie Xu, Xiangai Cheng. Ultrafast frequency shift of electromagnetically induced transparency in terahertz metaphotonic devices. Laser Photonics Rev 14(3): 1900338 (2020).

Article

Tong M Y, Hu Y Z, Xie X N, Zhu X G, Wang Z Y et al. Helicity-dependent THz emission induced by ultrafast spin photo-current in nod-al-line semimetal candidate Mg3Bi2. Opto-Electron Adv 3, 200023 (2020).

DOI: 10.29026/oea.2020.200023