Enhanced spin Hall effect of light in the PT-symmetric trilayer structure containing epsilon-near-zero materials

We systematically study the spin Hall effect of light (SHEL) in the parity-time (PT)-symmetric trilayer structure containing epsilon-near-zero (ENZ) materials, and design a high sensitivity refractive index sensor with an adjustable sensing range. It is revealed that the SHEL shift in the PT-symmetric trilayer structure is clearly enhanced, which is two orders of magnitude larger than that in the conventional sandwich structure containing ENZ materials. The enhancement of the SHEL shift is attributed to the fact that the change of reflection coefficient induced by the quasi-bound states in the continuum (quasi-BIC) in the former structure is smoother than that induced by the bound states in the continuum in the latter structure. It is further found that when the refractive index of the interlayer dielectric in the PT-symmetric structure is fixed, the SHEL shift is significantly enhanced near the quasi-BIC resonance angle determined by the gain-loss coefficient. Meanwhile, the SHEL shift enhanced by excitation of quasi-BIC is very sensitive to the gain-loss coefficient and the refractive index of the interlayer dielectric. Finally, we design a high sensitivity refractive index sensor with an adjustable sensing range based on the quasi-BIC-enhanced SHEL shift. These studies provide a pathway to enhance the SHEL and may open avenues for the application of optical sensors.