Theoretical Researches On The Photonic Spin Hall Effect Of Hyperbolic Materials

When a beam of linearly polarized light is reflected or refracted in a structure with a refractive index gradient,the beam splits into two circularly polarized beams（left-and right-circularly polarized light）in a direction perpendicular to the refractive index gradient,a phenomenon known as photonic spin Hall effect（PSHE）.The photonic spin Hall effect not only shows great application potential in the field of precision metrology,but also provides a new way to control photons for the design of micro-nan photonic devices,so it has received more and more attention in recent years.The photonic spin Hall effect is a weak effect.For conventional materials and structures,the lateral and longitudinal displacements are usually only a few tenths of the wavelength of the incident light,which greatly limits the practical applications of photonic spin Hall effect.At present,many researchers are working to enhance the photonic spin Hall effect by improving weak measurement techniques,exploring unconventional optical materials,and designing new resonance structures.The photonic spin Hall effect is a weak effect.For conventional materials and structures,the lateral and longitudinal displacements are usually only a few tenths of the wavelength of the incident light,which greatly limits the practical application of the photonic spin Hall effect.At present,many researchers are working to enhance the photonic spin Hall effect by improving weak measurement techniques,exploring unconventional optical materials,and designing new resonance structures.In this dissertation,one-dimensional photonic crystals andα-Li₃N-type topological semimetals based on two-dimensional transition metal sulfides are used as the research objects.The evolution of the photonic spin Hall effect with the wavelength（or photon energy）of the incident light,incident angle,film thickness and other physical parameters,and the regulation mechanism of the two materials on the photonic spin Hall effect is revealed.The specific research work and the research results obtained are as follows:（1）We study the photonic spin Hall effect on the surface of one-dimensional photonic crystals composed of ultrathin Au films,monolayer transition metal dichalcogenides（TMDCs）and defect layers.By adjusting the thickness of the Au film in the one-dimensional photonic crystal（variation range from 2.4 to 40.0 nm）,we found that the ultrathin Au film is more helpful to enhance the photonic spin Hall effect than the bulk Au film,especially when the thickness of the Au film is 4.4 nm,the lateral photon spin Hall shift is 37.94 times the wavelength of the incident light,which is higher than the maximum lateral photon spin Hall shift（3.05 times the wavelength）when the thickness of the Au film is 40.0 nm.12 times or more.In addition,among the four monolayer TMDCs（i.e.,Mo S₂,Mo Se₂,WS₂,WSe₂）,WS₂ is more suitable to be used to enhance the photonic spin Hall effect,which may be due to the more efficient short-range surface plasmons in ultrathin Au films.Inter-coupling with B exciton resonance in monolayer WS₂ is easy.In addition,the extreme value of the photon spin Hall shift usually appears near the indicated plasmon resonance（SPR）angle,when the thickness of the Au film is≤8.5 nm,the SPR angle appears around 33.0°,which is hardly affected by the wavelength change of the incident light;When the thickness of the Au film is≥13.0 nm,since the real part of the principal component of the effective dielectric constant of the one-dimensional photonic crystal satisfies Re（ε_|）Re（ε_⊥）<0 in a specific wavelength band（that is,the one-dimensional photonic crystal is in a specific wavelength band is a hyperbolic metamaterial）,so the SPR angle changes with the wavelength of the incident light,which in turn causes the extremum of the photon spin Hall shift to change with the wavelength of the incident light.（2）Some scholars have studied the electronic energy band structure ofα-Li₃N-type topological semimetals based on first-principles calculations.The results show thatα-Li₃N-type topological semimetals are natural hyperbolic materials.In this paper,we simulated the photon spin Hall effect of transmitted light after linearly polarized incident onα-Li₃N-type topological semi-metal films,and plotted the photon spin Hall displacement as a function of incident photon energy and incident angle.change spectrum.The simulation results show that the maximum or minimum value of the photon spin Hall shift spectrum appears on the side slightly higher than the transition energy between theα-Li₃N-type topological half-metal bands,and with the incident angle or the dielectric constant of the exit medium.increases with a redshift.When theα-Li₃N-type topological semimetal is subjected to compressive strain,the maximum or minimum value of the photonic spin Hall shift appears blue-shifted;in sharp contrast,tensile strain induces lattice expansion,leading to a maximum Values or minima appear redshifted.In addition,hole doping ofα-Li₃N and Li₂KN formed by replacing Li atoms with K atoms will cause lattice expansion,so hole doping and alloying will lead to the maximum or extreme value of the photon spin Hall shift.Small values appear redshifted.