Abstract-Enhanced Terahertz Radiation by Efficient Spin-to-Charge Conversion in Rashba-Mediated Dirac Surface States

 

Mingyu Tong, Yuze Hu, Zhenyu Wang, Tong Zhou, Xiangnan Xie, Xiang’ai Cheng, Tian Jiang

https://pubs.acs.org/doi/10.1021/acs.nanolett.0c03079

The enhancement of terahertz (THz) radiation is of extreme significance for the realization of the THz probe and imaging. However, present THz technologies are far from being enough to realize high-performance and room-temperature THz sources. Fortunately, topological insulators (TIs), with spin-momentum-locked Dirac surface states, are expected to exhibit a high terahertz emission efficiency. In this work, the novel concept of a Rashba-state-enhanced spintronic THz emitter is demonstrated on the basis of ferromagnet/heavy metal/topological insulator (FM/HM/TI) heterostructure. We find that the THz emission intensity changes as a function of HM interlayer thickness, and a 1.98 times higher intensity compared to that of FM/TI can be achieved when a meticulously designed thickness of the HM layer is inserted. The improvement of terahertz radiation is ascribed to the additive effect of Rashba splitting and topological surface states at the HM/TI interface. These results offer new possibilities for realizing spintronic THz emitters in TI-based magnetic heterostructures.

Abstract-Saturated absorption of different layered Bi2Se3 films in the resonance zone [Invited]

Jun Zhang, Tian Jiang, Tong Zhou, Hao Ouyang, Chenxi Zhang, Zheng Xin, Zhenyu Wang, and Xiang’ai Cheng

http://65.202.222.105/prj/abstract.cfm?uri=prj-6-10-C8

Here, we used the micro P-scan method to investigate the saturated absorption (SA) of different layered Bi2Se3${\mathrm{Bi}}_2{\mathrm{Se}}_3$ continuous films. Through resonance excitation, first, we studied the influence of the second surface state (SS) on SA. The second SS resonance excitation (∼2.07  eV$\sim 2.07\mathrm{eV}$) resulted in a free carrier cross section that was 4 orders of magnitude larger than usual. At the same time, we found that the fast relaxation process of the massless Dirac electrons is much shorter than that of electrons in bulk states. Moreover, the second SS excitation resonance reduced the saturation intensity. Second, we studied the effect of the thickness on the SA properties of materials. The results showed that the saturation intensity was positively correlated to the thickness, the same as the modulation depth, and the thicker the Bi2Se3${\mathrm{Bi}}_2{\mathrm{Se}}_3$ film was, the less the second SS would influence it. This work demonstrated that by using Bi2Se3${\mathrm{Bi}}_2{\mathrm{Se}}_3$ as a saturable absorber through changing the thickness or excitation wavelength, a controllable SA could be achieved.

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