【International Papers】Controlling the Propagation Asymmetry of Hyperbolic Shear Polaritons in Beta-Gallium Oxide

Researchers from the Vanderbilt University have published a dissertation titled " Controlling the propagation asymmetry of hyperbolic shear polaritons in beta-gallium oxide " in nature communication.

Abstract

Structural anisotropy in crystals is crucial for controlling light propagation, particularly in the infrared spectral regime where optical frequencies overlap with crystalline lattice resonances, enabling light-matter coupled quasiparticles called phonon polaritons (PhPs). Exploring PhPs in anisotropic materials like hBN and MoO₃ has led to advancements in light confinement and manipulation. In a recent study, PhPs in the monoclinic crystal β-Ga₂O₃ (bGO) were shown to exhibit strongly asymmetric propagation with a frequency dispersive optical axis. Here, using scanning near-field optical microscopy (s-SNOM), we directly image the symmetry-broken propagation of hyperbolic shear polaritons in bGO. Further, we demonstrate the control and enhancement of shear-induced propagation asymmetry by varying the incident laser orientation and polariton momentum using different sizes of nano-antennas. Finally, we observe significant rotation of the hyperbola axis by changing the frequency of incident light. Our findings lay the groundwork for the widespread utilization and implementation of polaritons in low-symmetry crystals.

Fig. 1: Real-space imaging of HShPs launching from infrared antenna on the surface of bGO observed via FEL-coupled s-SNOM.

Fig. 2: Dependence on illumination orientation of HShPs in a bulk bGO crystal.

Paper Link：https://www.nature.com/articles/s41467-023-40789-7