Finite-element simulations of hyperbolic plasmon polaritons in 1T’ WTe₂

Surface plasmon polaritons (SPPs) are high-momentum, spatially confined quasiparticles formed due to the collective oscillations of photons with electrons in metals or semiconductors. Recently, it was discovered that 1T’ WTe₂ supports hyperbolic SPPs with a unique hyperbola-shaped wavefront, allowing for efficient directional control. In this work, we systemically explore these hyperbolic modes with finite-element simulations. We found that hyperbolic SPPs in WTe₂ are sensitively dependent on excitation frequency, sample thickness, and temperature. Furthermore, when stacking two WTe₂ flakes together with a twist angle, the topology of hyperbolic SPPs can be effectively manipulated by varying the twist angle. At a certain critical angle, a topological transition occurs where hyperbolic SPPs start to evolve into normal elliptic SPPs. Our work uncovers the unique plasmonic responses of WTe₂ and opens a new research direction of twisted plasmonics.