The tunable topological valley states in designer surface plasmon crystals based on liquid crystals

Valley states, originating from 2D layered materials, have drawn much research attention and inspired enormous intriguing physical phenomenon, such as valley Hall effect, valley projected topological edge states and so on. Since valley has been extended into classical systems, some topological properties were deduced and observed in classical wave systems too. However, exploration of practical applications is still on the way due to fixed structure after fabrication. Therefore, in this work, we introduce a nematic LC into designer surface plasmon (DSP) crystal with valleys existing in its band structures, and change the refractive index of LC with external electric field to move the spectral position of topological valley states. Under the action of changeable refractive index, the bulk valley-selective chiral excitation and backscattering-immune broadband valley- projected edge transport have been numerically demonstrated.