Asymmetry spin-polarization Fermi arc and topological chiral beam splitter with the triply degenerate point in metamaterial.

Dirac points (DPs) and Weyl points (WPs) have received much attention in photonic crystals (PhCs) and three-dimensional (3D) metamaterials research due to the robust surface states and Fermi arcs. In this work, two pairs of triply degenerate points (TDPs) have been proposed in a 3D metamaterial by breaking the time reversal symmetry (T) with an external magnetic field. Based on these TDPs, two pairs of asymmetric surface states with spin-polarization are revealed, and a topological chiral beam splitter is demonstrated showing the different propagating directions of the right-handed polarization (RCP) and left-handed polarization (LCP) lights. Remarkably, we can achieve unidirectional propagation with RCP or LCP even excited by a linear source owing to the asymmetry surface state. Our work provides a new, to the best of our knowledge, platform to study spin-polarization surface states and the enhanced spin photonic Hall effect in the metamaterials.

Anomalous Electromagnetic Tunneling in Bianisotropic ϵ-µ-Zero Media.

Quantum tunneling, one of the most celebrated effects arising from the wave nature of matter, describes the partial penetration of an incident propagating wave through a potential barrier in the form of an evanescent field that exponentially decays from the incident interface. A similar tunneling effect has also been observed in classical systems, such as the frustrated total internal reflection. Here we reveal an unexplored form of tunneling for electromagnetic waves which features opposite behaviors for the electric and magnetic fields, with one turning into a growing field, and the other a decaying field, in a medium that exhibits both ϵ-µ-zero and bianisotropy. Our Letter provides a new mechanism for manipulating electromagnetic waves for novel device applications.

Observation of Non-Abelian Nodal Links in Photonics.

In crystals, two bands may cross each other and form degeneracies along a closed loop in the three-dimensional momentum space, which is called nodal line. Nodal line degeneracy can be designed to exhibit various configurations such as nodal rings, chains, links, and knots. Very recently, non-Abelian band topology was proposed in nodal link systems, where the nodal lines formed by consecutive pairs of bands exhibit interesting braiding structures and the underlying topological charges are described by quaternions. Here, we experimentally demonstrate non-Abelian nodal links in a biaxial hyperbolic metamaterial. The linked nodal lines threading through each other are formed by the crossings between three adjacent bands. Based on the non-Abelian charges, we further analyze various admissible nodal link configurations for the three-band system. On the interface between the metamaterial and air, surface bound states in the continuum are observed, which serves as the symmetry-enforced derivative of drumhead surface states from the linked nodal lines. Our work serves as a direct observation of the global topological structures of nodal links, and provides a platform for studying non-Abelian topological charge in the momentum space.

Tuning spontaneous radiation of chiral molecules by asymmetric chiral nanoparticles.

We have obtained analytical expressions for the radiative decay rate of the spontaneous emission of a chiral molecule located near a dielectric spherical particle with a chiral nonconcentric spherical shell made of a bi-isotropic material. Our numerical and graphical analyses show that material composition, thickness and degree of non-concentricity of the shell can influence significantly the spontaneous radiation of the chiral molecule. In particular, the radiative decay rates can differ in orders of magnitude for a chiral molecule located near the thin and thick parts of a nonconcentric shell as well as near a concentric shell made of chiral metamaterial. We also find that the radiative decay rates of the "right" and "left" chiral molecule enantiomers located near a nanoparticle with a chiral metamaterial shell can differ pronouncedly from each other. Our findings therefore suggest a way to tune the spontaneous emission of chiral molecules by varying the material composition, thickness and degree of non-concentricity of the shell in the nearby composite nanoparticle and also to enhance the chirality selection of chiral molecules in racemic mixtures.