Height dependent asymmetric propagations of polariton fields in twisted MoO₃ with an interlayer gap

Natural in-plane hyperbolic phonon polaritons with low-loss are emerging as an important platform for directional manipulations of electromagnetic fields at the sub-diffraction limit. Especially, further lowering of in-plane polariton symmetry enriches the freedom for sub-diffractional in-plane light manipulations. In this work, we demonstrate height dependent asymmetric propagations of in-plane polariton fields in twisted homostructures of MoO 3 with interlayer separation, where the existence of shear-like hyperbolic polaritons and usually symmetric polariton fields are observed at different heights of the homostructure. Our findings demonstrate the interlayer gap as a new degree of freedom for engineering polariton fields in the vertical direction, which is promising for designing novel compact photonic devices for intergraded photonics and thermal transport management.