Photonic nodal lines with quadrupole Berry curvature distribution

Abstract

In periodic systems, nodal lines are loops in the three-dimensional momentum space where two bands are degenerate with each other. Nodal lines exhibit rich topological features as they can take various configurations such as rings, links, chains and knots. These line nodes are usually protected by mirror or PT symmetry. Here we propose and demonstrate a novel type of photonic straight nodal lines in a D2d meta-crystal which are protected by roto-inversion time (roto-PT) symmetry. The nodal lines are located at the central axis and hinges of the Brillouin zone. They appear as quadrupole sources of Berry curvature flux and allow for the precise control of the quadrupole strength. Interestingly, there exist topological surface states at all three cutting surfaces, as guaranteed by the pi-quantized Zak phases along all three directions. As frequency changes, the surface state equi-frequency contours evolve from closed to open contours, and become straight lines at a critical transition frequency, at which diffraction-less surface wave propagation are demonstrated, paving way towards development of super-imaging photonic devices.

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Cited by in corpus (5)

• A brief review of topological photonics in one, two, and three dimensions
• Experimental demonstration of non-adjacent band topology connecting multiple nodal links
• Demonstration of non-Abelian frame charge flow in photonic crystals
• Intrinsic triple degeneracy point bounded by nodal surfaces in chiral photonic crystal
• Floquet-Engineering Weyl Points and Linked Fermi Arcs from Straight Nodal Lines