van der Waals heterostructures of atomically thin layers with rotational misalignments, such as twisted bilayer graphene, feature interesting structural moiré superlattices. Because of the quantum coupling between the twisted atomic layers, light-matter interaction is inherently chiral; as such, they provide a promising platform for chiral plasmons in the extreme nanoscale. However, while the interlayer quantum coupling can be significant, its influence on chiral plasmons still remains elusive. Here we present the general solutions from full Maxwell equations of chiral plasmons in twisted atomic bilayers, with the consideration of interlayer quantum coupling. We find twisted atomic bilayers have a direct correspondence to the chiral metasurface, which simultaneously possesses chiral and magnetic surface conductivities, besides the common electric surface conductivity. In other words, the interlayer quantum coupling in twisted van der Waals heterostructures may facilitate the construction of various (e.g., bi-anisotropic) atomically-thin metasurfaces. Moreover, the chiral surface conductivity, determined by the interlayer quantum coupling, determines the existence of chiral plasmons and leads to a unique phase relationship (i.e., ±π/2 phase difference) between their transverse-electric (TE) and transverse-magnetic (TM) wave components. Importantly, such a unique phase relationship for chiral plasmons can be exploited to construct the missing longitudinal spin of plasmons, besides the common transverse spin of plasmons.
Bibliographical noteFunding Information:
This work was sponsored by NSF/EFRI-1741660 the Singapore Ministry of Education [Grants No. MOE2018-T2-1-022(S), No. MOE2016-T3-1-006], Spain’s MINECO under Grants No. FIS2017-82260-P, No. PGC2018-096955-B-C42, No. CEX2018-000805-M as well as by the CSIC Research Platform on Quantum Technologies PTI-001, and Germany’s Deutsche Forschungsgemeinschaft (DFG) via SFB 1277. This work at Zhejiang University was sponsored by the National Natural Science Foundation of China (NNSFC) under Grants No. 61801426, No. 61625502, No. 11961141010, and No. 61975176, the Top-Notch Young Talents Program of China, the Zhejiang Provincial Natural Science Foundation under Grants No. Z20F010018, and the Fundamental Research Funds for the Central Universities.
© 2020 American Physical Society.