The pseudo-magnetic field, an artificial synthetic gauge field, has attracted intense research interest in the classical wave system. The strong pseudo-magnetic field is realized in a two-dimensional photonic crystal (PhC) by introducing the uniaxial linear gradient deformation. The emergence of the pseudo-magnetic field leads to the quantization of Landau levels. The quantum-Hall-like edge states between adjacent Landau levels are observed in our designed experimental implementation. The combination of two reversed gradient PhCs gives rise to the spatially nonuniform pseudo-magnetic field. The propagation of the large-area edge state and the interesting phenomenon of the snake state induced by the nonuniform pseudo-magnetic field is experimentally demonstrated in a PhC heterostructure. This provides a good platform to manipulate the transport of electromagnetic waves and to design useful devices for information processing.
Since the discovery of topology, many works have been focused on periodic lattice systems, where both short-and long-range order are taken into consideration. Here, we construct a two-dimensional amorphous photonic crystal possessing short-range order, but its level of long-range order can be controlled, and experimentally investigate the transport of topological edge states in this amorphous system. We demonstrate that topology properties still remain with unidirectional edge states propagation, immune to specific disorder strength. This proposed amorphous configuration provides new opportunities to explore the relationship of the short-range order only and topology and may alleviate the fabrication difficulties to topological optical devices for practical applications.
Two anisotropic exceptional points (EPs) of arbitrarily high order are found in a class of random non-Hermitian systems, where the non-Hermiticity emerges from non-reciprocal hoppings. Both eigenvalues and phase rigidity show different asymptotic forms near the anisotropic EP in two orthogonal directions in the parameter space, making them anisotropic EPs. The critical exponents of phase rigidity follow universal rules near an anisotropic EP, and the exponents depend on the dimension of the Hamiltonian as well as the approaching direction, but are independent of the random configurations. We found multiple ellipses formed by EPs of order two converge to the two high-order EPs in the parameter space. A ring of high-order EPs is formed when all ellipses coalesce for some particular configurations.
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