Abstract
The extensive research of two-dimensional layered materials has revealed that valleys, as energy extrema in momentum space, could offer a new degree of freedom for carrying information. Based on this concept, researchers have predicted valley-Hall topological insulators that could support valley-polarized edge states at non-trivial domain walls. Recently, several kinds of photonic and sonic crystals have been proposed as classical counterparts of valley-Hall topological insulators. However, direct experimental observation of valley-polarized edge states in photonic crystals has remained difficult until now. Here, we demonstrate a designer surface plasmon crystal comprising metallic patterns deposited on a dielectric substrate, which can become a valley-Hall photonic topological insulator by exploiting the mirror-symmetry-breaking mechanism. Topological edge states with valley-dependent transport are directly visualized in the microwave regime. The observed edge states are confirmed to be fully valley-polarized through spatial Fourier transforms. Topological protection of the edge states at sharp corners is also experimentally demonstrated.
Highlights
The extensive research of two-dimensional layered materials has revealed that valleys, as energy extrema in momentum space, could offer a new degree of freedom for carrying information
Regarding the classical counterparts of this kind of quantum topological electronic system, several photonic crystals have been proposed as possible valley-Hall photonic topological insulators (PTIs) and numerically investigated[16,17,18,19]
We introduce a perturbation to break the ΓK-mirror symmetry of the unit cell, which will lift the degeneracy at the valleys and open a bandgap[20,49]
Summary
The extensive research of two-dimensional layered materials has revealed that valleys, as energy extrema in momentum space, could offer a new degree of freedom for carrying information. In order to achieve direct observations, the edge states need to be vertically confined in free space to eliminate covers[27], and the elimination of covers is beneficial for both manufacturing and applications In view of these demands, designer surface plasmons (DSPs), dubbed spoof surface plasmons[28,29,30,31,32,33,34,35,36,37,38,39], can become a potential platform for constructing valley-Hall PTIs. DSPs are non-leaky electromagnetic (EM) surface modes similar to the famous surface plasmons at optical and infrared regimes but arise at much lower frequencies in periodic subwavelength metallic structures, and these structures can be called DSP crystals. The valley-Hall PTI should have potential in applications considering its planar geometry and ultrathin thickness and may serve as a prototype for future development of telecommunication devices
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
