Abstract-Tailoring anisotropic perfect absorption in monolayer black phosphorus by critical coupling at terahertz frequencies

Ye Ming Qing, Hui Feng Ma, and Tie Jun Cui

Fig. 1 (a) Schematic of the proposed structure. (b) Schematic of monolayer BP. (c) The single port resonator model in coupled mode theory. Frequency dependent surface conductivity along (d) the x-direction and (e) the y-direction. Solid lines and dashed lines denote the real part and imaginary part, respectively.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-25-32442

A metamaterial perfect absorber composed of a black phosphorus (BP) monolayer, a photonic crystal, and a metallic mirror is designed and investigated to enhance light absorption at terahertz frequencies. Numerical results reveal that the absorption is enhanced greatly with narrow spectra due to critical coupling, which is enabled by guided resonances. Intriguingly, the structure manifests the unusual polarization-dependent feature attributable to the anisotropy of black phosphorus. The quality factor of the absorber can be as high as 95.1 for one polarization while 63.5 for another polarization, which is consistent with the coupled wave theory. The absorption is tunable by varying key parameters, such as period, radius, slab thickness, incident angle, and polarization angle. Furthermore, the state of the system (i.e., critical coupling, over coupling, and under coupling) can be tuned by changing the electron doping of BP, thus achieving various applications. This work offers a paradigm to enhance the light-matter interaction in monolayer BP without plasmonic response, and this easy-to-fabricate structure will provide potential applications in BP-based devices.

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