Research On Dynamically Controlled Asymmetric Spin Splitting Of Light Beam Based On Graphene Materials

When the linearly polarized beam is reflected or refracted on the interface of the medium,the left-and right-handed circular polarization components will produce a spin-dependent splitting shift in the center of gravity.This phenomenon is called the photonic spin Hall effect(SHE),which is caused by the spin-orbit coupling of light.Generally,the spin shift values of the left-and right-handed circular polarization components are equal.However,if left-and right-handed circularly polarized light components are given different spin-orbit coupling effects,asymmetric spin splitting will occur,which is a general extension of the symmetrical photonic SHE.So far,the photonic SHE has been studied in different materials,such as graphene,anisotropic crystals,metamaterials,superinterfaces,metals etc.The photonic SHE has potential applications in the fields of precision measurement,quantum information processing,spin-based nanophotonics devices,and so on.Therefore,it is very necessary to effectively control this physical phenomenon.At present,there is no effective method to manipulate asymmetric spin splitting: because the physical parameters of materials are difficult to dynamically change,the characteristics of asymmetric splitting are fixed and cannot be dynamically adjusted.In this work,we propose a simple and effective method to realize the dynamic control of the asymmetric spatial and angular shifts in the plane of the reflected beam by constructing a glass-graphene-air structure model.The specific research content is as follows:(1)It is proposed that graphene dynamically regulates the asymmetric spin displacement of the photonic SHE,without changing the device structure,and can dynamically control the asymmetric splitting only by using an external electric field.We analyzed the asymmetric splitting in the beam propagation model of the graphene film-coated glass-air interface.The study found that when the beam is reflected near the Brewster angle and the total internal reflection angle,by changing the Fermi energy level in the graphene,the asymmetric spatial and angular shifts in the plane can be significantly adjusted.Interestingly,when the incident state of the beam is horizontally polarized,the spin displacement is more sensitive to changes in the Fermi level near the Brewster angle than to the total internal reflection angle.The discovery of these asymmetric spin-related splits provides new ideas for spin photonics.(2)It is proposed to use the spin shift to directly detect the tiny Fermi level changes of graphene.This work analyzed the relationship between the angular shift and the Fermi level,and found that the Fermi level change in the range of 0.25 to 1e V can be directly detected by observing the large and sensitive numerical changes of the angular shift.The method of measuring the Fermi level of graphene provides a potential application for the design of novel nanophotonic devices(such as optical sensors).