Twist-angle and thickness-ratio tuning of plasmon polaritons in twisted bilayer van der Waals films

TL;DR

This study demonstrates that the topology of plasmon polaritons in twisted bilayer WTe2 films can be effectively tuned by adjusting both the twist angle and the thickness ratio, expanding control over nanophotonic properties.

Contribution

It introduces the thickness ratio as a new parameter for manipulating plasmonic topology in bilayer van der Waals materials, complementing the twist angle control.

Findings

Plasmon topology can be modified by TR and TA adjustments.

Effective sheet conductivity explains topological transitions.

TR provides an additional degree of freedom for plasmon control.

Abstract

Stacking bilayer structures is an efficient way to tune the topology of polaritons in in-plane anisotropic films, e.g., by leveraging the twist angle (TA). However, the effect of another geometric parameter, film thickness ratio (TR), on manipulating the plasmon topology in bilayers is elusive. Here, we fabricate bilayer structures of WTe2 films, which naturally host in-plane hyperbolic plasmons in the terahertz range. Plasmon topology is successfully modified by changing the TR and TA synergistically, manifested by the extinction spectra of unpatterned films and the polarization dependence of the plasmon intensity measured in skew ribbon arrays. Such TR- and TA-tunable topological transitions can be well explained based on the effective sheet optical conductivity by adding up those of the two films. Our study demonstrates TR as another degree of freedom for the manipulation of plasmonic topology in nanophotonics, exhibiting promising applications in bio-sensing, heat transfer and the enhancement of spontaneous emission.