Optical rotation in chiral van der Waals stacks

Two-dimensional (2D) van der Waals heterostructures offer a unique opportunity to design nanodevices with desired optical properties [1]. Chiral nanostructures may manifest optical activity: when light is transmitted through... [ view full abstract ]

Two-dimensional (2D) van der Waals heterostructures offer a unique opportunity to design nanodevices with desired optical properties [1]. Chiral nanostructures may manifest optical activity: when light is transmitted through such system its polarization plane is rotated. Recent experiments showed that the polarization rotation angle in the twisted bilayer graphene is several orders of magnitude larger than in natural materials [2].

Here we present the theory, which describes light transmittance through chiral stacks of 2D van der Waals monolayers, such as transition metal dichalcogenides (TMDC). The structure consists of a sequence of monolayers with strong exciton resonance [3], where each layer is rotated with respect to the precedent by a certain angle (Fig. 1). Due to low (chiral) symmetry such structure demonstrates optical activity and circular birefringence, although a single TMDC monolayer does not. Our calculations show that polarization rotation angle in realistic structures can reach 10 degrees per micrometer. Frequency dependence of polarization rotation angle reveals resonances at the energies of the eigen exciton modes of the stack. Interestingly, the resonances corresponding to both the superradiant symmetric mode and “dark” exciton modes are of the similar magnitude. Note that the “dark” modes that interact weakly with light are usually hidden in the optical transmittance and reflectance spectra. Therefore, spectra of optical rotation can be used to visualize the complete set of exciton modes in van der Waals stacks.

This work was supported by the Government of the Russian Federation (Project No. 14.W03.31.0011).

[1] A.K. Geim and I.V. Grigorieva, Nature 499,419 (2013).

[2] C.-J. Kim et al., Nat. Nanotechnol. 11, 520 (2016).

[3] C.Robert et al., Phys Rev. B 93, 205423 (2016).