Photonic Spin Hall Effect In Two-dimensional Atomic Crystals

When photon is reflected or refracted at the dielectric interface,there exists a photonic spin Hall effect similar to the electronic Hall effect,in which the dielectric refractive index gradient plays the role of the external field,the beam or wave packet undergos a spin-dependent shift perpendicular to the direction of the refractive index gradient.As photons can be an important carrier of information and energy in present day,the study of the photonic spin Hell effect may lead to the generation of new photonic devices.This is the same as the electronic Hall effect leading to the idea of developing new electronic elements in scientific community.Morever,a new subject called spinphotonics is being developed,like the spintronics.In recent years,the photonic spin Hall effect in various physical systems has been widely studied.However,the study of the photonic spin Hall effect in two-dimensional atomic crystals is absent.As the two-dimensional atomic crystal has only one or several layers of atomic structure,most of the physical properties,effects and parameters change very small in such a condition,which can be regarded as a weak effect.In addition,since its scale has reached the scope of the micro system,many quantum effects have emerged and even play a leading role under some conditions.This will be a challenge for the traditional measurements.The findings in this paper are shown as follow:(1)An modified weak measurement theory is proposed to detect the photonic spin Hall effect in the condition of the wave function being disturbed.The modified weak measurement theory model is established,and compared with the experimental results,it shows that the modified weak measurement theory is more accurate than the traditional weak measurement theory.The modified theory is valid not only in the regime of weak spin-orbit coupling of light,but also in the strong-coupling regime,especially in the intermediate regime.This research is of great significance for the detection of photonic spin Hall effect in strong or intermediate regime.(2)The weak Goos-H?nchen effect in graphene was observed via the amplification effect of weak value in weak measurement.The expression of small GH displacement in graphene was theoretically obtained.The amplification and measurement of the GH shift was experimently realized.The experimental results are compared with the theoretical results,and the correctness of the zero-thickness model of the two-dimensional atomic crystal is verified.In addition,it is found that the amplified GH shift is very sensitive to the number of graphene layers,which can be used to determine the number of graphene layers conveniently and accurately.(3)Photonic spin Hall effect in the graphene-substrate system under the external magnetic field is studied.It is found that the in-plane and transverse spin-dependent splittings in photonic spin Hall effect exhibit different quantized behaviors.The quantized in-plane and transverse spin-dependent splittings is calculated and analyzed in detail.It is shown that the quantized photonic spin Hall effect can be described as the result of the quantized geometric phase(Berry phase),which corresponds to the quantized spin-orbit interaction.In addition,an experimental scheme based on quantum weak value amplification is proposed to detect the quantized photonic spin Hall effect in terahertz frequency regime.Combined with the quantum weak measurement technique,the quantized photonic spin Hall effect holds great promise for measuring the quantum Hall conductivity and Berry phase in graphene.Also,these studies may establish the relation between the electronic spin Hall effect in graphene and the photonic spin Hall effect.(4)The photonic spin Hall effect can be regarded as a direct optical analogy of the electronic spin Hall effect in an electronic system,where the refractive index gradient acts as an external field.However,experiments have shown that effective refractive index can not adequately explain the interaction between light and matter in atomically thin crystals.We study the spin-orbit interaction on the surface of a two-dimensional atomic crystal,and establish a model that does not involve the effective refractive index,which can accurately describe the spin-orbit interaction in the two-dimensional atomic crystal and the photonic spin Hall effect.Considering the freestanding two-dimensional atomic crystal,we theoretically predict a great photonic spin Hall effect induced by the strong spin-orbit interaction of light.This phenomenon can be explained as the large polarization rotation of the plane wave component in order to satisfy the transversality of the photon polarization.