We propose an ultra-thin metamaterial constructed by an ensemble of the same type of anisotropic aperture antennas with phase discontinuity for wave front manipulation across the metamaterial. A circularly polarized light is completely converted to the cross-polarized light which can either be bent or focused tightly near the diffraction limit. It depends on a precise control of the optical-axis profile of the antennas on a subwavelength scale, in which the rotation angle of the optical axis has a simple linear relationship to the phase discontinuity. Such an approach enables effective wave front engineering within a subwavelength scale.

Here, we investigate the spin-induced manipulation of orbitals using metasurfaces constructed from geometric phase elements. By carrying the spin effects to the orbital angular momentum, we show experimentally the transverse angular splitting between the two spins in the reciprocal space with metasurface, as a direct observation of the optical spin Hall effect, and an associated global orbital rotation through the effective orientations of the geometric phase elements. Such spin-orbit interaction from a metasurface with a definite topological charge can be geometrically interpreted using the recently developed high order Poincaré sphere picture. These investigations may give rise to an extra degree of freedom in manipulating optical vortex beams and orbitals using "spin-enabled" metasurfaces.

Metamaterials have shown to support the intriguing phenomenon of asymmetric electromagnetic transmission in the opposite propagation directions, for both circular and linear polarizations. In the present article, we propose a criterion on the relationship among the elements of transmission matrix, which allows asymmetrical transmission for linearly polarized electromagnetic radiation only while the reciprocal transmission for circularly one. Asymmetric hybridized metamaterials are shown to satisfy this criterion. The influence from the rotation of the sample around the radiation propagation direction is discussed. A special structure design is proposed, and its characteristics are analyzed by using numerical simulation.

We show that metamaterials can be used as a testing ground to investigate spontaneous symmetry breaking associated with non-Hermitian quantum systems. By exploring the interplay between near-field dipolar coupling and material absorption or gain, we demonstrate various spontaneous breaking processes of the PT -symmetry for a series of effective Hamiltonians associated to the scattering matrix. By tuning the coupling parameter, coherent perfect absorption, laser action and gain-induced complete reflection (π reflector) by using an ultrathin metamaterial can be obtained. Moreover, an ideal PT -symmetry can be established effectively in a passive system by exploring the balance between scattering and absorption loss using metamaterials.

Herein, the method of hydrometallurgy is adopted to recycle the precious metal cobalt in spent lithium ion batteries (LIBs).