Controlling the propagation asymmetry of hyperbolic shear polaritons in beta-gallium oxide

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 quasi-particles called phonon polaritons (PhPs). Exploring PhPs in anisotropic materials like hBN andMoO(3) has led to advancements in light confinement and manipulation. In a recent study, PhPs in the monoclinic crystal ss-Ga2O3 (bGO) were shown to exhibit strongly asymmetric propagation with a frequency dispersive optical axis. Here, using scanning near-field optical microscopy (sSNOM), 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.

Automated summary

The properties of phonon polaritons (PhPs) in the monoclinic crystal ss-Ga2O3 (bGO) were investigated, and strongly asymmetric propagation and frequency dispersive optical axis were observed. The symmetry-broken propagation of hyperbolic shear polaritons in bGO was directly imaged using scanning near-field optical microscopy (sSNOM). The control and enhancement of shear-induced propagation asymmetry were demonstrated by varying the incident laser orientation and polariton momentum using different sizes of nano-antennas, and significant rotation of the hyperbola axis was observed by changing the frequency of incident light. These findings lay the groundwork for the widespread utilization and implementation of polaritons in low-symmetry crystals.