Abstract-Tunable THz generalized Weyl points

Zhiping Yin, Fujia Chen, Kai Guo, Fei Shen, Keya Zhou, Jun Gao, Shutian Liu, and Zhongyi Guo

Fig. 1 Realization of Weyl points in a synthetic space. (a) Photonic crystals (PCs) with different p, q values. p and q form a parameter space, which determines the geometric structure of PCs. The inset shows one unit cell of the PC, where the first and the third layers are made of 5CB LCs (cyan), and the second and the forth layers are made of PDMS (gray). The thickness of each layer is related to its position in the p-q parameter space. (b) The band dispersion of PCs with two layers in one unit cell (red dash line) and four layers in one unit cell (blue solid line). Crossing points appear inside four layers’ dispersion. Here, 𝑑𝑎=125𝑢𝑚,$d_a=125um,$ 𝑑𝑏=35𝑢𝑚,$d_b=35um,$ and 𝑝=𝑞=0.$p=q=0.$ (c) The dispersion of PCs in the p-q space with 𝑘=0.5𝑘0,$k=0.5k_0,$ and 𝑘0=𝜋/(𝑑𝑎+𝑑𝑏).$k_0=\pi /\left(d_a+d_b\right).$ Here, two bands form a conical intersection. Panels (b) and (c) together show that the band dispersions are linear in all directions around the degenerated point in synthetic space, so we call it generalized Weyl point. (d) The equal frequency contours around generalized Weyl point in p-q space and its charge “-1”.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-2-512

Weyl points, as linearly double degenerated point of band structures, have been extensively researched in electronic and classical wave systems. However, Weyl points’ realization is always accompanied with delicate “lattice structures”. In this work, frequency-tunable terahertz (THz) generalized Weyl points inside the parameter space have been investigated and displayed by a specially designed photonic crystal with polydimethylsiloxane (PDMS) immersed in 4-cyano’-pentylbipenyl (5CB) liquid crystals (LCs). The reflective phase vortices as a signature of the generalized Weyl points are observed through our numerically simulations. Besides, interface states between photonic crystals and any reflective substrates are fulfilled too. Meanwhile, we could also change the orientation of LC molecule by the external magnetic field so as to tune the frequency of the first two bands’ Weyl point from 0.27698THz to 0.30013THz. This band lies in the short-range wireless communication. Thus, our proposal may be beneficial to the investigation and application of Weyl points’ properties and strongly localized states.

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