Topological multipolar corner state in a supercell metasurface and its interplay with two-dimensional materials

Abstract

Second-order topological insulators (SOTIs) have recently attracted much attention due to their capability to support lower-dimensional topological states, namely, the corner states. Here, we demonstrate that properly designed supercell metasurfaces can support photonic corner states, meanwhile further serving as an ideal platform for the implementations of topological polaritons and dynamically reconfigurable corner states by assembling two-dimensional materials. Such metasurfaces consist of an array of finite-sized SOTIs mimicking the two-dimensional Su–Schrieffer–Heeger model. We reveal that the topological transition happens in unit cells without the bandgap, and nondegenerate multipolar corner states emerge in the supercell metasurface due to the inter- and intrasupercell coupling effects. Especially since these corner states are above the light line of the metasurface, we realize the collective stimulation of the two dipolar corner states and their superposition state via far-field excitation. By stacking monolayer hexagonal boron nitride film onto the metasurface, we further achieve the topological phonon polaritons through the strong coupling between the corner state and the phonon, which is confirmed by the Rabi splitting as well as anticrossing behavior emerging in the transmission spectra. Furthermore, we reveal the robustness of the corner state and strong coupling by introducing defects into the metasurface. Finally, tunable corner state and strong coupling with on-demand control are realized by assembling monolayer graphene onto the metasurface. Our theoretical study proposes a unique hybrid-material platform for topological polaritonics and reconfigurable topological photonics, which can promote large-area topological applications in practice.

Single photon emitter deterministically coupled to a topological corner state

“…Moreover, the inherent polarization selection property of the corner state cavity offers the potential to significantly enhance the convenience of resonance fluorescence (RF) measurements and even surpass the conventional limit of 50% orthogonal RF efficiency 4 , 5 . In addition, the topological corner states can be extended into other quantum emitters 38 , 51 . While more complex corner states 52 can be utilized to enhance the excitation process 11 .…”

Polarization-independent second-order photonic topological corner states

“…where P j is determined by the parity η associated with π rotation at Γ and X(Y) points and the summation is over all the occupied bands below the bandgap. Here, P x is equal to P y , namely, P x = P y , due to the C 4 symmetry [35,36]. Eigenfield patterns at the X point of the two bands for TM and TE modes are shown in Figs.…”

Tailoring topological corner states in photonic crystals by near- and far-field coupling effects

“…[21,22] Interestingly, these corner states exhibit exotic characteristics such as nondegenerate eigenfrequencies and collective behaviors,caused by near-field coupling. Moreover, such arrays provide a versatile platform for studying the topological lightmatter interaction, [23] having potential applications in largearea topological photonic devices. However, these studies have involved only PhC hole slabs so far, where another typical PhC slab, the rod slab, is still missing.…”