Observation Of Topological Edge States Research Articles

Coexistence of giant Rashba spin splitting and quantum spin Hall effect in H–Pb–F

Rashba spin splitting (RSS) and quantum spin Hall effect (QSHE) have attracted enormous interest due to their great significance in the application of spintronics. In this work, we theoretically proposed a new two-dimensional (2D) material H–Pb–F with coexistence of giant RSS and quantum spin Hall effec by using the ab initio calculations. Our results show that H–Pb–F possesses giant RSS (1.21 eV⋅Å) and the RSS can be tuned up to 4.16 eV⋅Å by in-plane biaxial strain, which is a huge value among 2D materials. Furthermore, we also noticed that H–Pb–F is a 2D topological insulator (TI) duo to the strong spin–orbit coupling (SOC) interaction, and the large topological gap is up to 1.35 eV, which is large enough for for the observation of topological edge states at room temperature. The coexistence of giant RSS and quantum spin Hall effect greatly broadens the potential application of H–Pb–F in the field of spintronic devices.

Exploring topology of 1D quasiperiodic metastructures through modulated LEGO resonators

We investigate the dynamics and topology of metastructures with quasiperiodically modulated local resonances. The concept is implemented on a LEGO beam featuring an array of tunable pillar-cone resonators. The versatility of the platform allows the experimental mapping of the Hofstadter-like resonant spectrum of an elastic medium, in the form of a beam waveguide. The non-trivial spectral gaps are classified by evaluating the integrated density of states of the bulk bands, which is experimentally verified through the observation of topological edge states localized at the boundaries. Results also show that the spatial location of the edge states can be varied through the selection of the phase of the resonator's modulation law. The presented results open new pathways for the design of metastructures with functionalities going beyond those encountered in periodic media by exploiting aperiodic patterning of local resonances and suggest a simple, viable platform for the observation of a variety of topological phenomena.

Observation of topological edge states induced solely by non-Hermiticity in an acoustic crystal

Most existing non-Hermitian topological systems derive their nontrivial topology from Hermitian factors. Here, the authors report on the experimental observation of acoustic topological edge states induced solely by non-Hermiticity. They show that non-Hermiticity is able to create a topological band gap from a gapless Hermitian system. The study offers the possibilities for actively steerable topological wave manipulations in applications ranging from acoustics to photonics.

Direct observation of topological edge states in silicon photonic crystals: Spin, dispersion, and chiral routing

Topological protection in photonics offers new prospects for guiding and manipulating classical and quantum information. The mechanism of spin-orbit coupling promises the emergence of edge states that are helical, exhibiting unidirectional propagation that is topologically protected against back scattering. We directly observe the topological states of a photonic analog of electronic materials exhibiting the quantum spin Hall effect, living at the interface between two silicon photonic crystals with different topological order. Through the far-field radiation that is inherent to the states' existence, we characterize their properties, including linear dispersion and low loss. We find that the edge state pseudospin is encoded in unique circular far-field polarization and linked to unidirectional propagation, thus revealing a signature of the underlying photonic spin-orbit coupling. We use this connection to selectively excite different edge states with polarized light and directly visualize their routing along sharp chiral waveguide junctions.

Observation of Topological Edge States at the Step Edges on the Surface of Type-II Weyl Semimetal TaIrTe4.

Topological materials harbor topologically protected boundary states. Recently, TaIrTe4, a ternary transition-metal dichalcogenide, was identified as a type-II Weyl semimetal with the minimal nonzero number of Weyl points allowed for a time-reversal invariant Weyl semimetal. Monolayer TaIrTe4 was proposed to host topological edge states, which, however, lacks of experimental evidence. Here, we report on the topological edge states localized at the monolayer step edges of the type-II Weyl semimetal TaIrTe4 using scanning tunneling microscopy. One-dimensional electronic states that show substantial robustness against the edge irregularity are observed at the step edges. Theoretical calculations substantiate the topologically nontrivial nature of the edge states and their robustness against the edge termination and layer stacking. The observation of topological edge states at the step edges of TaIrTe4 surfaces suggests that monolayer TaIrTe4 is a two-dimensional topological insulator, providing TaIrTe4 as a promising material for topological physics and devices.

Dynamically reconfigurable topological edge state in phase change photonic crystals

The observation of topological edge states (TESs) revolutionized our understanding of scattering and propagation of electromagnetic (EM) waves. Supported by topological robustness, the TES at the interface between trivial and non-trivial insulators was not reflected from the structural disorders and imperfections. Recently topological photonic crystals (PhCs) were demonstrated to obtain remarkable one-way propagation of the TES, having the advantages of lossless propagation, dense integration, and high fabrication tolerance over conventional PhCs. Nevertheless, the lack of reversible switching of TES possesses significant limitations in helicity/spin filtering and tunable photonic devices. We proposed a topological PhC based on a prototypical phase-change material, Ge2Sb2Te5 (GST225) to solve the problem. We find that at a particular frequency, the TES within the structure can be reversibly switched between “on” and “off” by transiting the GST225 structural state between amorphous and crystalline. Moreover, the topology of the PhC was maintained since the tuning of TES was achieved by varying the refractive index of GST225 instead of the structural geometry. This provides a continuous change of the spectral position of the photonic bandgap and TES by gradually crystallising the GST225. We show that the phase change of GST225 from amorphous to crystalline and vice versa can be engineered in nanoseconds. Our proof of concept may offer a platform for dynamically tuning the TESs that might otherwise be challenging to attain in photonic systems. We expect it to have potential applications for photonic devices in topological optical circuits and scatter-free one-way light propagation.

Observation of topological edge states of acoustic metamaterials at subwavelength scale

Topological states are of key importance for acoustic wave systems owing to their unique transport properties. In this study, we develop a hexagonal array of hexagonal columns with Helmholtz resonators to obtain subwavelength Dirac cones. Rotation operations are performed to open the Dirac cones and obtain acoustic valley vortex states. In addition, we calculate the angular-dependent frequencies for the band edges at the K-point. Through a topological phase transition, the topological phase of pattern A can change into that of pattern B. The calculations for the bulk dispersion curves show that the acoustic metamaterials exhibit BA-type and AB-type topological edge states. Experimental results demonstrate that a sound wave can transmit well along the topological path. This study could reveal a simple approach to create acoustic topological edge states at the subwavelength scale.

Observation of topological edge states in parity–time-symmetric quantum walks

Spontaneous parity–time-symmetry breaking and topological edge states are observed in a photonic non-Hermitian system — a quantum walk interferometer.

Mapping plasmonic topological states at the nanoscale.

We report on the first experimental observation of topological edge states in zigzag chains of plasmonic nanodisks. We demonstrate that such edge states can be selectively excited with the linear polarization of the incident light, and visualize them directly by near-field scanning optical microscopy. Our work provides experimental verification of a novel paradigm for manipulating light at the nanoscale in topologically nontrivial structures.