Highly Tunable Interlayer Coupling and Electronic Structures of Few-Layer Graphene with Pressure.

The interlayer electronic coupling is responsible for the electronic structure evolution from monolayer graphene to graphite and for the moiré potential in twisted bilayer graphene. Here we demonstrate that the interlayer transfer integral (hopping parameter) increases nearly 40% with a quite moderate pressure of ∼3.5 GPa, manifested by the resonance peak shift in the infrared spectra of all 2-10 L graphene. A simple model based on the Morse potential enabled us to establish the relationship between the transfer integral and pressure. Our work provides fundamental insights into the dependence of the electronic coupling on the interlayer distance.

Tunable anisotropic van der Waals films of 2M-WS2 for plasmon canalization.

In-plane anisotropic van der Waals materials have emerged as a natural platform for anisotropic polaritons. Extreme anisotropic polaritons with in-situ broadband tunability are of great significance for on-chip photonics, yet their application remains challenging. In this work, we experimentally characterize through Fourier transform infrared spectroscopy measurements a van der Waals plasmonic material, 2M-WS2, capable of supporting intrinsic room-temperature in-plane anisotropic plasmons in the far and mid-infrared regimes. In contrast to the recently revealed natural hyperbolic plasmons in other anisotropic materials, 2M-WS2 supports canalized plasmons with flat isofrequency contours in the frequency range of ~ 3000-5000 cm-1. Furthermore, the anisotropic plasmons and the corresponding isofrequency contours can be reversibly tuned via in-situ ion-intercalation. The tunable anisotropic and canalization plasmons may open up further application perspectives in the field of uniaxial plasmonics, such as serving as active components in directional sensing, radiation manipulation, and polarization-dependent optical modulators.