Electromagnetic Impurity-Immunity Induced by Parity-Time Symmetry

Impurities usually play an important role in modifying the bulk properties of electronic or electromagnetic materials. In this work, we demonstrate a way to break this discipline and realize the extraordinary physical property of impurity-immunity, which leads to perfect transmission irrespective of embedded impurities of almost any material and shape. This extraordinary property comes from the exceptional points of a pair of parity-time (PT)-symmetric metasurfaces sandwiching a slab of epsilon-near-zero medium. By systematically investigating the PT-symmetric metasurfaces sandwiching a slab of dielectrics or metamaterials, we obtain the two complementary solutions of exceptional points corresponding to perfect transmission. Interestingly, when the permittivity of the slab approaches zero, the two solutions of exceptional points coalesce into one exceptional point. At such a critical point, we find that the original "doping" effect of impurities in epsilon-near-zero media, proposed by Nader Engheta's group very recently [I. Liberal et al., Science 355, 1058 (2017)], is significantly suppressed. Our work shows that exceptional points can be used to eliminate scattering of impurities in a bulk medium.