  Optical systems that respect Parity-Time (PT) symmetry can be realized with
proper incorporation of gain/loss materials. However, due to the absence of
magnetic response at optical frequencies, the wave impedance is defined
entirely by their permittivity and, hence, the PT-symmetric character is
controlled solely via their refractive index. Here, we show that the separate
control of the wave impedance enabled by metamaterials can grant access to
further tuning of the Exceptional Points, appearance of mixed phases
(coexistence of PT-symmetric and PT-broken phases) and occurrence of phase
re-entries, not easily realizable with natural materials.
