Institute of Acoustics, Tongji University, Shanghai 200092, China.
Phys Rev Lett. 2023 Mar 17;130(11):116101. doi: 10.1103/PhysRevLett.130.116101.
Chirality is one of the fundamentals of nature with strong ties to asymmetry. In wave physics, it is conventionally characterized by asymmetric scattering of circularly polarized waves but suffers from two-state polarization. To overcome the limitation, here we demonstrate the concept of extreme chirality regarding orbital angular momentum (OAM) helicity, originating from a chiral quasibound state in the continuum held by a mirror-symmetry-broken metasurface. Empowered by the intrinsic OAM-selective coupling nature of the metasurface, the system arrives at a peculiar state where the left-handed incident vortex is completely absorbed while the right-handed counterpart is totally reflected, namely, a perfectly-chiral exceptional point. The realization of asymmetric OAM modulation creates the possibility to explore chirality with unlimited states. Our work raises a new paradigm for the study of extreme OAM chirality and enriches the physics of chiral wave-matter interaction.
手性是自然界的基本属性之一，与非对称性密切相关。在波动物理学中，手性通常表现为圆偏振波的不对称散射，但存在二态极化的问题。为了克服这一限制，我们展示了一种关于轨道角动量（OAM）螺旋的极端手性的概念，该概念源于由非对称镜面对称性破缺超表面支撑的连续体中的手性准束缚态。借助超表面的固有 OAM 选择性耦合特性，该系统达到了一个奇特的状态，即左手入射涡旋完全被吸收，而右手入射涡旋则完全被反射，即完美手性的异常点。不对称 OAM 调制的实现为探索具有无限状态的手性创造了可能性。我们的工作为研究极端 OAM 手性提出了一个新的范例，并丰富了手性波物质相互作用的物理。
