Abstract
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 $\;{{\pm 45}}^\circ$ 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 $\theta$ are sensitive to the concentrations of the BSA solution.
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