Broadband and wide-angle nonreciprocity with a non-Hermitian metamaterial

We theoretically demonstrate a non-Hermitian metamaterial exhibiting broadband and wide-angle nonreciprocity. The metamaterial consists of planar metal-dielectric layers with a parity-time (PT ) symmetric distribution of loss and gain. With increasing loss and gain, the band structure and band gap are strongly modified; further, the PT potential leads to distinct internal field distributions when illuminated from different sides. Including nonlinearities arising from natural loss and gain saturation leads to nonreciprocal transmission in the visible over a 50-nm wavelength and ±60^∘ angular range.