Gao Y, Kaushik S, Philip E J, Li Z, Qin Y, Liu Y P, Zhang W L, Su Y L, Chen X, Weng H, Kharzeev D E, Liu M K, Qi J
State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 611731, China.
Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, 11794, USA.
Nat Commun. 2020 Feb 5;11(1):720. doi: 10.1038/s41467-020-14463-1.
Weyl semimetals host chiral fermions with distinct chiralities and spin textures. Optical excitations involving those chiral fermions can induce exotic carrier responses, and in turn lead to novel optical phenomena. Here, we discover strong coherent terahertz emission from Weyl semimetal TaAs, which is demonstrated as a unique broadband source of the chiral terahertz wave. The polarization control of the THz emission is achieved by tuning photoexcitation of ultrafast photocurrents via the photogalvanic effect. In the near-infrared regime, the photon-energy dependent nonthermal current due to the predominant circular photogalvanic effect can be attributed to the radical change of the band velocities when the chiral Weyl fermions are excited during selective optical transitions between the tilted anisotropic Weyl cones and the massive bulk bands. Our findings provide a design concept for creating chiral photon sources using quantum materials and open up new opportunities for developing ultrafast opto-electronics using Weyl physics.
外尔半金属中存在具有不同手性和自旋纹理的手性费米子。涉及这些手性费米子的光激发可以诱导奇异的载流子响应，进而导致新颖的光学现象。在此，我们发现了来自外尔半金属TaAs的强相干太赫兹辐射，它被证明是手性太赫兹波的独特宽带源。太赫兹辐射的偏振控制是通过光电流效应调节超快光电流的光激发来实现的。在近红外区域，由于占主导地位的圆光电流效应导致的与光子能量相关的非热电流，可归因于在倾斜的各向异性外尔锥和有质量的体能带之间的选择性光学跃迁过程中，手性外尔费米子被激发时能带速度的剧烈变化。我们的发现为利用量子材料创建手性光子源提供了一种设计理念，并为利用外尔物理开发超快光电子学开辟了新机遇。
