Giant photonic spin Hall effect in bilayer borophene metasurfaces

Particle nature of the photonic spin Hall effect

It is widely recognized that light exhibits a wave-particle duality. However, the explanation for the photonic spin Hall effect (PSHE) primarily relies on the wave nature of light as dictated by Maxwell's Equations. There is a lack of exploration into the particle nature of light in this regard. In this context, we offer a fresh interpretation of the PSHE from the perspective of particle nature of light. For the out-of-plane PSHE, the spin shifts result from the macroscopic manifestation of the conservation of spin-orbital angular momentum of one photon. For the in-plane PSHE, the spin shifts arise from the spread of in-plane wavevector. Based on the wave nature of light, we also obtain the same spin shifts, confirming the consistency of the wave-particle duality of light. Furthermore, we find that the spin shifts of the PSHE are not the overall displacement of photons with the same handedness, but the outcome of coherent superposition among photons of the same handedness. These discoveries further enhance our comprehension of the fundamental nature of the PSHE.

Giant photonic spin Hall effect induced by hyperbolic shear polaritons

Recently, broken symmetry within crystals has been attracting tremendous research interest since it can be utilized to effectively manipulate the propagation of photons. In particular, low-symmetry Bravais crystals can support hyperbolic shear polaritons (HShPs), holding great promise for technological upgrading in the emerging research area of spinoptics. Herein, an Otto-type multilayer structure consisting of a KRS5 prism, a sensing medium, and monoclinic β-Ga₂O₃ crystals is designed to ameliorate the photonic spin Hall effect (PSHE). The surface of β-Ga₂O₃ is the monoclinic (010) plane (x-y plane). We show that giant spin Hall shifts with three (or two) orders of magnitude of the incident wavelength can be obtained in the in-plane (or transverse) directions. The azimuthal dispersions of photonic spin Hall shifts present non-mirror-symmetric patterns upon tuning the rotation angle of β-Ga₂O₃ around the z-axis in the plane. All of these exotic optical properties are closely correlated with the broken crystal lattice symmetry and the incurred excitation of HShPs in monoclinic β-Ga₂O₃ crystals. By virtue of the remarkably enhanced PSHE, our proposed Otto-type multilayer structure shows a superior biosensing performance in which the maximum sensitivity is two orders of magnitude larger than that of previously reported PSHE biosensors based on two-dimensional materials. In addition, the optimized physical and structural parameters including the incident angle, excitation wavelength, azimuth angle and doping concentration of β-Ga₂O₃, thickness and refractive index of sensing medium are also investigated and presented. This work unequivocally confirms the strong influence of crystal symmetry on the PSHE, providing important insights into understanding the rich modulation of spin-orbit interactions of light via shear polaritons and therefore facilitating potential applications in photoelectronic devices.