Giant circular dichroism induced by tunable metamirror with Dirac semimetal

Circular dichroism (CD) is widely applied in chemistry and biology, because chiral molecules can be detected and distinguished by analyzing the value of CD in the terahertz (THz) spectrum, which covers the characteristic spectrum of semiconductors, plasmas, and biomolecules. However, traditional metal metastructures cannot tune the wavelength of CD peaks continuously without changing the geometric parameters, which limits its practical application. In this paper, a three-layer tunable metastructure is proposed with giant CD in the THz spectrum. This structure consists of a gold substrate and two different bulk Dirac semimetal (BDS) bars. Its CD value up to 0.969 can be obtained by simulation. By adjusting the Fermi energy of BDS, the wavelength of CD peaks is tunable in the range of 12 µm without a change in geometric parameters. Furthermore, a theoretical analysis is used to explain the blueshift of the CD peaks while Fermi energy is increased. Moreover, the effect of some structural changes on CD values has also been studied. This work can pave the way to designing a CD detector or related device in the THz spectrum.