Superdirective leaky radiation from a PT-synthetic metachannel

Spectral singularities appearing in parity-time (PT)-symmetric non-Hermitian optical systems have aroused a growing interest due to their new exhilarating applications, such as bifurcation effects at exceptional points and the coexistence of coherent perfect absorber and laser (so-called CPAL point). We introduce here how the concept of CPAL action provoked in PT-symmetric metasurfaces can be translated into practical implementation of a low-loss zero/low-index open channel supporting a nearly undamped fast-wave propagation. Such a PT-synthetic metachannel shows the capability to produce a high-directivity leaky radiation, with a tunable beam angle that depends on the gain-loss parameter. The proposed structure may enable new kinds of super-directivity antennas, as well as many applications that demand extreme dielectric properties, such as epsilon-near-zero (ENZ).