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At photonic Dirac points, electromagnetic waves are governed by the same equations as two-component massless relativistic fermions. However, photonic Dirac points are known to occur in pairs in "photonic graphene" and other similar photonic crystals, which necessitates special precautions to excite only one valley state. Systems hosting unpaired photonic Dirac points are significantly harder to realize, as they require broken time-reversal symmetry. Here, we report on the observation of an unpaired Dirac point in a planar two-dimensional photonic crystal. The structure incorporates gyromagnetic materials, which break time-reversal symmetry; the unpaired Dirac point occurs when a parity-breaking parameter is fine-tuned to a topological transition between a photonic Chern insulator and a conventional photonic insulator phase. Evidence for the unpaired Dirac point is provided by transmission and field-mapping experiments, including a demonstration of strongly non-reciprocal reflection. This unpaired Dirac point may have applications in valley filters and angular selective photonic devices. 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Controlling the load of Co-CoFe 2 O 4 can receive exceptional impedance matching. • The minimum reflection loss is −65.31 dB at 2.1 mm. • The maximum effective absorption bandwidth is 8.48 GHz at 2.4 mm. Carbon nanomaterials have attracted a great deal of attention in various fields especially in electromagnetic wave absorption due to unique physical and chemical properties. Herein, a novel Co-CoFe 2 O 4 @mesoporous hollow carbon spheres (PCHMs) nanocomposites were prepared by two-facile steps, which included synthesizing three-dimensional mesoporous hollow carbon nanospheres (3D PCHMs) by hard template method, pyrolysis and etching process and in-situ growth of ultra-small Co-CoFe 2 O 4 nanoparticles on PCHMs. The microscopic morphology and electromagnetic wave absorption mechanisms were discussed in depth. The synthesized Co-CoFe 2 O 4 @PCHMs maintained a stable hollow and mesoporous structure and the Co-CoFe 2 O 4 nanoparticles are uniformly distributed on the PCHMs. The complex permittivity and complex permeability could be effortlessly controlled by the content of Co-CoFe 2 O 4 nanoparticles. Benefitting from the remarkable impedance matching under the influence of moderate complex permittivity and complex permeability, the minimum reflection loss (RL min) of S2 exhibited −65.31 dB at 2.1 mm. The maximum effective absorption bandwidth (EAB) reached up to 8.48 GHz. The Co-CoFe 2 O 4 @PCHMs nanocomposites will have great potential application in electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • The 2D MXene-based accordion-like hybrid structure was obtained. • Controlling the addition of Ti 3 C 2 T x can effectively control the dielectric parameters. • The effective bandwidth is up to 4.24 GHz with a matched thickness of 1.5 mm. Owing to their unique structure and high dielectric loss, two-dimensional transition metal carbides and nitrides (MXenes) are widely used in electromagnetic wave absorption. The novel Co 9 S 8 /C/Ti 3 C 2 T x hybrid material with a multilayer structure was successfully fabricated by hydrothermal and annealing processes. The unique multilayered hybrid material is assembled from Ti 3 C 2 T x film layers, Co 9 S 8 particles, and carbon flakes. The Co 9 S 8 particles were uniformly anchored on Ti 3 C 2 T x and carbon flakes. The Co 9 S 8 /C/Ti 3 C 2 T x -100 hybrid material has demonstrated impressive electromagnetic absorption performance after the multi-component introduction and interface design were optimized. Besides, the hybrid material exhibits the maximum reflection loss of −50.07 dB at 7.6 GHz under a matched thickness of 2.51 mm, and the effective absorption bandwidth (RL ≤ -10 dB) is covered 4.24 GHz. The synergistic effect of dielectric and magnetic loss, interfacial polarization, and multilayer structure was beneficial to the improvement of electromagnetic wave absorption performance. This research provides a simple demonstration of the design and synthesis of high-performance MXenes-based absorbing materials. [ABSTRACT FROM AUTHOR]