Study On Parity-time(PT) Symmetry Breaking Of Terahertz Metasurface Structures

In 1998,Bender first proposed the Parity-Time(PT)symmetric quantum theory,explained the relationship between the non-Hermitian Hamiltonian with PT symmetry and the real energy spectrum,and extended the research of quantum mechanics to the non-Hermitian range.Until 2007,Ganainy et al.,found that the paraxial approximation equation was highly consistent with the Schr?dinger equation in quantum mechanics,thus PT symmetry was introduced into optics from quantum mechanics,and PT symmetry theory has been greatly developed in the field of optics.Then,according to the PT symmetry phase transition conditions,people use various methods to dynamically regulate the PT symmetrical system,such as using superconductor niobium nitride,phase change material Gete,graphene,photosensitive silicon or changing the angle of incident light.Although these methods can well realize PT symmetric phase transition,there are still some difficulties in experiments.Combined with the above reasons,we propose a scheme to realize PT phase transition by dropping protein solution on the split ring resonator.Specific research details are as follows:1.In this paper,we propose a PT symmetric metasurface system whose unit cell consists of two orthogonal directional split ring resonators(SRRs)with the same resonant frequency but different loss coefficients.Different from the gain-loss non-Hermitian structure,the metasurface in this paper is a full loss system.2.Different from the typical method of changing the distance of metasurface SRRs,PT symmetry phase transition was realized by dropping bovine serum albumin(BSA)solution of different concentrations on the metasurface.The theoretical and experimental results show that when BSA solution of different concentrations are dropped on the PT metasurface,the eigenstate of the PT system will change from circularly polarization state at exceptional point(EP)to elliptical polarization state with two major axes along ±45°,which indicates that PT symmetry phase transition has taken place in the system.3.In addition,with the change of the concentration of BSA solution,the transmission spectrum and elliptical angle of the measured samples also change and through calculation,the sensitivity of the system is 323 GHz/RIU,which indicate that the system has potential application value in biosensors.