Active Valley-topological Plasmonic Crystal in Metagate-tuned Graphene

Abstract

A valley plasmonic crystal for graphene surface plasmons (GSPs) is proposed. We demonstrate that a designer metagate, placed within a few nanometers from graphene, can be used to impose a triangular periodic Fermi energy landscape on the latter. For specific metagate geometries and bias voltages, the combined metagate-graphene structure is shown to produce sufficiently strong Bragg scattering of GSPs to produce complete propagation bandgaps, and to impart the GSPs with nontrivial valley-linked topological properties. Valley-selective kink states supported by a domain wall between differently patterned metagates are shown to propagate without reflections along sharply curved interfaces owing to suppressed inter-valley scattering. Our approach paves the way for non-magnetic dynamically reconfigurable topological nanophotonic devices.

Slow and robust plate acoustic waveguiding with valley-dependent pseudospins

“…1(b) by the flip of the energy band at the high-symmetry point K due to the lack of inversion symmetry. 23,24) At the point K, two energy extreme points (red solid dots) are formed at the upper and lower edges of the band gap, corresponding to two (K) valley modes, labeled modes I and II, respectively. Displacement fields of the two modes corresponding to phases from 0 to π are shown in Fig.…”

“…The existence of chiral elastic energy flow is an important characteristic of valley modes, which can be analogues of a kind of pseudospin. 18,23,24) By utilizing these pseudospins, researchers have realized electromagnetic [1][2][3]25) and acoustic transmission lines [5][6][7][8]26) with robust valley-dependent transport.…”

Guiding robust valley-dependent edge states by surface acoustic waves

“…The constitutive parameters of analogue to pseudospin. 26,30,31 By utilizing these valley-induced pseudospins, researchers have achieved electromagnetic [15][16][17]32 and acoustic transmission line [19][20][21][22]33 with robust, valley-dependent transport of wave energy. The valley states with different elastic vortex fields can be selectively excited by appropriate chiral sources.…”