Saturday, September 23, 2017

Abstract-Terahertz surface emission of d-band electrons from a layered tungsten disulfide crystal by surface field

Longhui Zhang, Yuanyuan Huang, Qiyi Zhao, Lipeng Zhu, Zehan Yao, Yixuan Zhou, Wanyi Du, and Xinlong Xu

Terahertz (THz) time-domain emission spectroscopy in both transmission and reflection configurations has been employed to understand the THz radiation property and surface properties of tungsten disulfide (WS2). We observed only one polarization of THz radiation under different polarization of pump beam and a saturation effect with the increasing of pump power. The results are different from that of MoS2\thinspace based on optical rectification in spite of similar physical and optoelectronic properties of them. The nonlinear optical coefficient calculation based on first-principle method combined with the azimuthal angle dependence of THz radiation implies that THz radiation is insensitive to the azimuthal angle in WS2. From the pump polarization angle dependence of THz radiation, we find that the contribution due to the nonlinear effect is only 12{\%} approximately. All these suggest the main THz mechanism from WS2 is due to the surface depletion field induced by the surface states. We also analyzed the surface field features of WS2 with the maximum surface depletion field of approximate 1.2 \texttimes 105 V/cm. Fresnel law combined with the dipole radiation model is also used to analyze the angular dependence of THz radiation. The results can not only afford a fundamental THz radiation property of layered materials, but also promote the development of THz devices based on layered materials.

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