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Vanishing Chern numbers usually mean that a system is topologically trivial, but this rule may be violated for periodically driven systems. Here, Maczewskyet al.report topologically protected edge modes in a periodically driven photonic lattice with all bands of zero Chern number.

The conventional implementation of parity-time symmetry relies on the interplay of gain and loss. Here, Bentzien et al. present a novel approach towards non-Hermiticity that leverages nonorthogonal modes in coupled waveguides explicitly avoiding the use of either gain or loss.

By introducing a further modal dimension to transform a two-dimensional photonic waveguide array, a photonic topological insulator with protected topological surface states in three dimensions, enabled by a screw dislocation, is demonstrated.

To date, experimental demonstrations of PT-symmetric systems have been restricted to one dimension. Here, the authors experimentally realize and characterize a two-dimensional PT-symmetric system using photonic lattice waveguides with judiciously designed refractive index landscape and an alternating loss distribution.

Counter-propagating chiral edge states are demonstrated in a photonic structure able to effectively incorporate fermionic time-reversal symmetry, thus providing the photonic implementation of an electronic topological insulator.

Departing from common approaches to designing Floquet topological insulators, here the authors present a photonic realization of Floquet topological insulators revealing topological phases that simultaneously support Chern and anomalous topological states.

The authors propose a non-Hermitian topological insulator with a real-valued energy spectrum based on a periodically driven Floquet model implemented in a photonic platform where generalized parity–time symmetry is protected against spontaneous symmetry breaking under a spatiotemporal gain and loss distribution.

The behaviour of multi-dimensional excitation dynamics and localization transition is synthesized in one-dimensional lattices formed by planar photonic structures.

Optical guiding by a synthetic gauge field is experimentally demonstrated through an array of evanescently coupled identical waveguides, opening the door to applications of artificial gauge fields in optical, microwave and acoustic systems and in cold atoms.

The nonlinear properties of photonic topological insulators remain largely unexplored, as band topology is linked to linear systems. But nonlinear topological corner states and solitons can form in a second-order topological insulator, as shown by experiments.

Established to explain high-energy particle physics, supersymmetry has since been invoked to describe the interplay between symmetry and topology in numerous fields. Here, supersymmetric transformations are shown theoretically and experimentally to destroy and restore topology in a photonic crystal.