We experimentally demonstrate a topological transition of classical light in "photonic graphene": an array waveguides arranged the honeycomb geometry. As system is uniaxially strained (compressed), two unique Dirac points (present spectrum conventional graphene) merge and annihilate each other, band gap forms. result, edge states are created on zigzag destroyed bearded edge. These results applicable for any 2D honeycomb-type structure, from carbon-based graphene to photonic lattices crystals.

Advances in topological photonics and non-Hermitian optics have drastically changed our perception on how interdisciplinary concepts may empower unprecedented applications. Bridging the two areas could uncover reciprocity between topology non-Hermiticity complex systems. So far, such endeavors focused mainly linear-optics regime. Here, we establish a nonlinear platform for control of parity-time (PT) symmetry edge states. Experimentally, demonstrate that optical nonlinearity effectively...

Abstract Higher-order topological insulators (HOTIs) are recently discovered phases, possessing symmetry-protected corner states with fractional charges. An unexpected connection between these and the seemingly unrelated phenomenon of bound in continuum (BICs) was unveiled. When nonlinearity is added to HOTI system, a number fundamentally important questions arise. For example, how does couple higher-order BICs rest including states? In fact, thus far nonlinear HOTIs have remained...

Abstract The orbital degrees of freedom play a pivotal role in understanding fundamental phenomena solid-state materials as well exotic quantum states matter including superfluidity and topological semimetals. Despite tremendous efforts engineering synthetic cold-atom, electronic photonic lattices to explore physics, thus far high orbitals an important class materials, namely, higher-order insulators (HOTIs), have not been realized. Here, we demonstrate $$p$$ <mml:math...

Abstract A hallmark of symmetry-protected topological phases are boundary states, which immune to perturbations that respect the protecting symmetry. It is commonly believed any perturbation destroys such a phase simultaneously states. However, by introducing and exploring weaker sub-symmetry requirement on perturbations, we find nature state protection in fact more complex. Here demonstrate states protected only sub-symmetry, using Su–Schrieffer–Heeger breathing kagome lattice models, even...

Pseudospin, an additional degree of freedom inherent in graphene, plays a key role understanding many fundamental phenomena such as the anomalous quantum Hall effect, electron chirality and Klein paradox. Unlike spin, pseudospin was traditionally considered unmeasurable quantity, immune to Stern-Gerlach-type experiments. Recently, however, it has been suggested that graphene is real angular momentum might manifest itself observable but so far direct tests remained unfruitful. Here, by...

We report the first experimental demonstration of localized flat-band states in optically induced Kagome photonic lattices. Such lattices exhibit a unique band structure with lowest being completely flat (diffractionless) tight-binding approximation. By taking advantage linear superposition eigenmodes lattices, we demonstrate high-fidelity transmission complex patterns such two-dimensional pyrochlore-like structures. Our numerical simulations find good agreement observations, upholding...

We present a simple, yet effective, approach for optical induction of Lieb photonic lattices, which typically rely on the femtosecond laser writing technique. Such lattices are established by judiciously overlapping two sublattices (an "egg-crate" lattice and square lattice) with different periodicities through self-defocusing photorefractive medium. Furthermore, taking advantage superposition localized flat-band states inherent in we demonstrate distortion-free image transmission such...

Abstract For decades, singular beams carrying angular momentum have been a topic of considerable interest. Their intriguing applications are ubiquitous in variety fields, ranging from optical manipulation to photon entanglement and microscopy coronagraphy free-space communications, detection rotating black holes even relativistic electrons strong-field physics. In most applications, however, travel naturally along straight line, expanding during linear propagation or breaking up nonlinear...

Flatband systems typically host "compact localized states" (CLS) due to destructive interference and macroscopic degeneracy of Bloch wave functions associated with a dispersionless energy band. Using photonic Lieb lattice (LL), such conventional flatband states are found be inherently incomplete, the missing modes manifested as extended line that form noncontractible loops winding around entire lattice. Experimentally, we develop continuous-wave laser writing technique establish finite-sized...

The flourishing of topological photonics in the last decade was achieved mainly due to developments linear photonic structures. However, when nonlinearity is introduced, many intriguing questions arise. For example, are there universal fingerprints underlying topology modes coupled by nonlinearity, and what can happen invariants during nonlinear propagation? To explore these questions, we experimentally demonstrate nonlinearity-induced coupling light into topologically protected edge states...

Abstract Flat-band systems have attracted considerable interest in different branches of physics the past decades, providing a flexible platform for studying fundamental phenomena associated with completely dispersionless bands within whole Brillouin zone. Engineered flat-band structures now been realized variety systems, particular, field photonics. localization, as an important phenomenon solid-state physics, is fundamentally interesting exploration exotic ground-state properties many-body...

We demonstrate both experimentally and theoretically controlled acceleration of one- two-dimensional Airy beams in optically induced refractive-index potentials. Enhancement as well reduction beam are realized by changing the index gradient, while shape is maintained during propagation through linear optical potential. Our results active manipulation graded media pertinent to Airy-type various environments.

We propose and demonstrate an approach for image signal transmission based on self-accelerating Airy beams. The spatial information is encoded in the Fourier space through a 4-f telescope system, which can circumvent obstacles to realize self-bending transmission. Furthermore, be retrieved from beams after propagation disordered scattering medium. Our experimental results agree well with theoretical predictions.

Topological properties of lattices are typically revealed in momentum space using concepts such as the Chern number. Here, we study unconventional loop states, namely, noncontractible states (NLSs) and robust boundary modes, mediated by nontrivial topology real space. While play a key role understanding fundamental physics flatband systems, their experimental observation has been hampered because challenge realizing desired conditions. Using laser-writing technique, optically establish...

Type-II Dirac/Weyl points, although impermissible in particle physics due to Lorentz covariance, were uncovered condensed matter physics, driven by fundamental interest and intriguing applications of topological materials. Recently, there has been a surge exploration such generic points using various engineered platforms including photonic crystals, waveguide arrays, metasurfaces, magnetized plasma polariton micropillars, aiming towards relativistic quantum emulation understanding exotic...

We study both theoretically and experimentally the effect of nonlinearity on topologically protected linear interface modes in a photonic Su-Schrieffer-Heeger (SSH) lattice. It is shown that under either focusing or defocusing nonlinearity, this topological mode SSH lattice turns into family gap solitons. These solitons are stable. However, they exhibit only low amplitude power thus weakly nonlinear, even when bandgap wide. As consequence, if initial beam has modest high power, it will...

Cutting a honeycomb lattice (HCL) ends up with three types of edges (zigzag, bearded, and armchair), as is well known in the study graphene edge states. Here, we propose demonstrate distinctive twig-shaped edge, thereby observing new states using photonic platform. Our main findings are (i) twig generic type HCL complementary to armchair formed by choosing right primitive cell rather than simple cutting or Klein modification; (ii) form complete flat band across Brillouin zone zero-energy...

We demonstrate theoretically and experimentally that a finite Airy beam changes its trajectory while maintaining acceleration in nonlinear photorefractive media. During this process, the spatial spectrum reshapes dramatically, leading to negative (or positive) spectral defects on initial distribution under self-focusing defocusing) nonlinearity.

As one of the representatives emerging metallic transition-metal dichalcogenides, niobium ditelluride (NbTe2) has attracted intensive interest recently due to its distorted lattice structure and unique physical properties. Here, we report on ultrafast carrier dynamics in NbTe2 measured using time-resolved pump–probe transient reflection spectroscopy. A thickness-dependent relaxation time is observed, exhibiting a clear increase fast slow decay rates for thin flakes. In addition,...

Topological entities based on bulk-boundary correspondence are ubiquitous, from conventional to higher-order topological insulators, where the protected states typically localized at outer boundaries (edges or corners). A less explored scenario involves that inner boundaries, sharing same energy as bulk states. Here, we propose and demonstrate what refer "bulk-hole correspondence''-a relation between robust boundary modes (RBMs) existence of multiple "holes" in singular flatband lattices,...

Abstract Edge states in 2D materials are vital for advancements spintronics, quantum computing, and logic transistors. For uniform graphene, it is well known that the zigzag edges can host edge states, but realization of armchair has been challenging without engineered strain or breaking time‐reversal symmetry. Here, by using a photonic analog recently synthesized graphene‐like biphenylene network (BPN), topological in‐gap demonstrated, particularly at edges. Interestingly, several bulk...

Self-accelerating optical beams form as a direct outcome of interference, initiated by predesigned initial condition. In similar fashion, quantum mechanical particles exhibit force-free acceleration result interference effects following proper preparation the Schrodinger wave function. Indeed, is at heart such packets, and hence it implied that self-accelerating packets must be coherent entities. Counter to that, we demonstrate theoretically experimentally spatially incoherent beams, in both...

Abstract For the first time, a photonic super‐honeycomb lattice (sHCL) is established experimentally by use of continuous‐wave laser writing technique, and thereby two distinct flatband line states that manifest as noncontractible loop in an infinite are demonstrated. These localized (“straight” “zigzag” lines) observed sHCL with tailored boundaries cannot be obtained superposition conventional compact because they arise from real‐space topological property certain systems. In fact,...