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Parity-time symmetry for cloaking and negative refraction

We show that parity-time symmetry offers unique opportunities for achieving exciting phenomena, such as cloaking and negative refraction. By coating an object with a parity-time symmetric metasurface, i.e., a metasurface with appropriately balanced loss and gain, it is possible to achieve complete scattering cancellation for waves propagating along a particular direction. Similarly, bringing two metasurfaces with equal amounts of loss and gain close to each other allows obtaining negative refraction. Here we present the necessary conditions for achieving these functionalities and discuss the physical mechanisms involved. Furthermore, we study the dynamic response of such systems, and explore the relation between stability, bandwidth and object size.