Active control of parity-time symmetry phase transition in terahertz metasurface

Parity-time (PT) symmetry breaking in polarization space is investigated in a non-Hermitian terahertz metasurface system. In which the unit cell consists of two orthogonally oriented split-ring resonators with same resonant frequency but different loss coefficients. By tuning the conductivity of silicon island in the gap of one split-ring resonators, a phase transition is observable via both transmission spectra and polarization of the eigenstates. Specifically, as conductivity is 1600 Sm-1, the two eigentransmission spectra coincided and only a left circularly polarized state is obtained, indicating exceptional point appearance. For conductivity below and upon 1600 Sm-1, PT-symmetry and PT breaking regimes are separately provided. (C) 2021 Published by Elsevier B.V.