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THz integrate light sources represent an important building blocks for various applications. Here the authors report an electrically driven topological laser based on photonic Majorana zero mode that can convert electricity directly into THz single-mode laser with topologically nontrivial beams.

A combination of Floquet engineering and higher-order topological insulators has been lately only theoretically proposed. Here the authors experimentally realize an acoustic waveguides array to demonstrate a Floquet higherorder topological insulator extending its band topology from first order to higher order.

The distribution of Berry charge over a ring of exceptional points, called a Weyl exceptional ring, is experimentally demonstrated.

The concept of topological corner states in two dimensional topological insulators can be generalised to higher dimensions. Here, authors present a three dimensional acoustic metamaterial that exhibits the full hierarchy of topological multipole states including corner, hinge, surface and bulk states.

Observing the photonic analogue of an unpaired Dirac point is hard, as it requires breaking the time-reversal symmetry. Here, the authors use gyromagnetic materials to do that, and thus succeed in observing an unpaired Dirac point in a planar photonic crystal operating at microwave frequencies.

Here, the authors report on the experimental observation of a twofold symmetry enforced topological nodal surface in a 3D chiral acoustic crystal. The demonstrated nodal surface carries a topological charge of 2, constituting the first realization of higher-dimensional topologically-charged band degeneracy.

An unusual form of symmetry breaking in coupled microresonators with balanced optical gain and loss is now exploited to realize a novel type of optical isolator.

A second-order topological insulator in an acoustical metamaterial with a breathing kagome lattice, supporting one-dimensional edge states and zero-dimensional corner states is demonstrated.

Artificial magnetic fields have been meticulously engineered in a 3D acoustic crystal, facilitating the creation of 3D flat bands through Landau quantization of quasiparticles arising from nodal-ring band degeneracies.

Using a hexagonal array of helical waveguides, physicists have observed robust optical waves that move in one direction, bypassing obstacles and imperfections exactly as predicted by the theory of topological insulators. See Letter p.196

Higher-dimensional topological phases are predicted but cannot be realised in real materials as they are limited to three or fewer dimensions. Here, Wang et al. realise a four-dimensional topological insulator associated with a nonzero second Chern number using electric circuits.

Higher harmonic generation can be enhanced in left-handed nonlinear transmission lines. Here Wang et al. show that the presence of a topological edge state in a circuit analogue of the Su-Schrieffer-Heeger model can increase this enhancement even further.

The polarization, wavelength and power of a light wave can be simultaneously identified by a compact device made from twisted layers of carbon atoms — with a little help from an artificial neural network.

The limits of topological protection in photonic systems remain unclear. Here, Gao et al. construct photonic topological edge states and probe their robustness against a variety of defect classes, including some common time-reversal-invariant photonic defects that can break the topological protection.

Magnetically tunable three-dimensional photonic crystals are used to achieve the experimental demonstration of Chern vectors and their topological surface states, showing the Chern vector to be an intrinsic bulk topological invariant in three-dimensional topological materials.

In acoustic metamaterials, unconventional chiral quasiparticles exhibit multifold band degeneracy points, each carrying non-zero topological charges, giving rise to the topologically protected negative surface refraction.

The quantum Hall effect arises in two-dimensional electron systems and is characterized by current being carried by electrons along the edges of the system, in so-called chiral edge states (CESs), as a consequence of nontrivial topological properties of the bulk electronic band structure. Recently, it was theoretically predicted that electromagnetic analogues of CESs could be observed in photonic crystals; here, this is experimentally demonstrated.

A photonic crystal can realize an analogue of a valley Hall insulator, promising more flexibility than in condensed-matter systems to explore these exotic topological states.

Here, the authors show how Aurora kinase A (AURKA) employs Rab1a to direct ER remodeling. Activated Rab1A is retained on the ER and directly interacts with the RTN/REEP ER-shaping machinery to promote its oligomerization, eventually triggering an increase of ER complexity during mitosis.

Acoustic waveguides have been used to implement the long-theorized phenomenon of non-Abelian braiding, in which abstract geometric constructions are used to generate transformations between different modes.

A topological laser based on the valley degree of freedom in a compact photonic crystal can be pumped electrically, bringing topological physics concepts closer to real-life applications.

Photonic topological states can possess exceptional properties, but their protection is approximate, depending on the type of band topology. This Perspective clarifies these differences and explains their implications for technological applications.

By using a photonic synthetic lattice, it can be experimentally demonstrated that Dirac masses can be induced by means of non-Hermitian perturbations based on optical gain and loss.

Here, the authors introduce a 3D Weyl metamaterial hosting modes bound to a 1D topological lattice defect. The modes carry nonzero orbital angular momentum locked to the direction of propagation, and they experimentally demonstrate the ability to emit acoustic vortices into free space.

Topological lattice defects in topological materials offer a platform to explore a diverse range of phenomena, including fractional charges, chiral and gravitational anomalies, topological lasers and non-Hermitian skin effects. This Perspective article surveys the impact of these phenomena on condensed matter physics, photonics, acoustics and materials science.

Coherent perfect absorbers (CPAs) are electromagnetic structures in which the absorption of electromagnetic energy is assisted by the interference of incident waves. This Review summarizes the fundamental principles, implementations and promising applications of CPAs for the linear control of light with light.

A three-dimensional photonic topological insulator is presented, made of split-ring resonators with strong magneto-electric coupling, which has an extremely wide topological bandgap, forbidding light propagation.

Topological phenomena in photonics have been found of great importance in realizing advanced semiconductor laser. Here the authors demonstrate the manipulation of the light emission profiles from a Kekulé-modulated topological bulk cavity in a topological-protection manner, where the achieved lateral beam shifts in light polarizations could be useful for the laser design and photonic sensing applications.

In photonics, the introduction of order and disorder has traditionally been treated separately. However, recent developments in nanofabrication and design strategies have enabled the use of materials that lie between the extremes of order and disorder that can yield innovative optical phenomena. This Review surveys the basics and recent achievements of engineered disorder in photonics.

The optical and plasmonic properties of (Bi,Sb)₂(Te,Se)₃ trichalcogenide topological insulator crystals are studied systematically by first-principles density functional theory. These materials exhibit bulk plasmonic properties, dominated by interband transitions, which are better than gold and silver at blue and UV wavelengths. Moreover, topologically protected surface states are also capable of supporting propagating plasmon polariton modes over an extremely broad spectral range, due to a combination of interband and intraband transitions.