Experiment on parity-time-symmetry phase transition in non-Hermitian metasurfaces

Metasurfaces consisting of two orthogonally oriented split-ring resonators with the same resonant frequency but different loss coefficients are proposed to devise a parity-time (PT)-symmetry system. Bovine serum albumin (BSA) solutions with different concentrations are dropped onto the metasurfaces to the realize PT-symmetry phase transitions. Theoretical and experimental results show that eigenstates of the PT system will change from circularly polarized states at the exceptional point to corotating ellipses along ± 45 ∘ when the samples are from the bare metasurfaces to these with BSA, indicating phase transitions. Additionally, potential application of the system in a biosensor is illustrated as the transmission and ellipticity angle θ are sensitive to the concentrations of the BSA solution.