Tunable multifunctional terahertz coding metasurfaces based on Dirac semimetals

With the advent of digitally coding metasurfaces, it is easy to design functional devices and facilitates the manipulation of terahertz waves through specific arrays of digital particles. However, it is still very difficult to fabricate metasurfaces that can change their scattering patterns in the terahertz (THz) range. In this work, we design a 2-bit coding metasurface by varying the Fermi level (EF) of Dirac semimetal films (DSFs). Without changing the size of the metasurface, we implement mutual switching between four units (???0,??? ???1,??? ???2,??? and ???3??? elements) by changing the EF of the DSF. Different control functions of terahertz waves with different digital sequences are designed in advance, such as beam splitting, offset, mirror, anomalous reflection, convolution, generation of vortex beams and vortex convolution. The two-dimensional and three-dimensional far-field patterns simulated by CST Studio Suite were in line with our predictions. Our work shows how to make metasurface functional devices more diverse in the terahertz range using a dynamic tuning method.