Observation of unidirectional backscattering-immune topological electromagnetic states
By Z. Wang, Y. Chong, John D. Joannopoulos, Marin Soljačić. Nature, 2009
2,709 citations recorded by the source corpus.
One of the most striking phenomena in condensed-matter physics is the quantum Hall effect, which arises in two-dimensional electron systems subject to a large magnetic field applied perpendicular to the plane in which the electrons reside. In such circumstances, current is carried by electrons along the edges of the system, in so-called chiral edge states (CESs). These are states that, as a consequence of nontrivial topological properties of the bulk electronic band structure, have a unique directionality and are robust against scattering from disorder. Recently, it was theoretically predicted that electromagnetic analogues of such electronic edge states could be observed in photonic crystals, which are materials having refractive-index variations with a periodicity comparable to the wavelength of the light passing through them. Here we report the experimental realization and observation of such electromagnetic CESs in a magneto-optical photonic crystal fabricated in the microwave regime. We demonstrate that, like their electronic counterparts, electromagnetic CESs can travel in only one direction and are very robust against scattering from disorder; we find that even large metallic scatterers placed in the path of the propagating edge modes do not induce reflections. These modes may enable the production of new classes of electromagnetic device and experiments that would be impossible using conventional reciprocal photonic states alone. Furthermore, our experimental demonstration and study of photonic CESs provides strong support for the generalization and application of topological band theories to classical and bosonic systems, and may lead to the realization and observation of topological phenomena in a generally much more controlled and customizable fashion than is typically possible with electronic systems.
Subfields: Atomic and Molecular Physics, and Optics
View Paper: https://www.semanticscholar.org/paper/67f6126040381d0b5c89376892a65a7df4fff918
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In Atomic and Molecular Physics, and Optics
Citations in the corpus
- Observation of second-order topological insulators in sonic crystals (2018, background): “These gapless edge states are dictated by the topological invariants associated with the quantization of generalized Berry’s phases of the bulk energy bands through the bulk-edge correspondence, a paradigm that can also be extended to acoustic and photonic systems [5-23].”
- Photonic crystal nanocavity based on a topological corner state (2018, methodology): “Indeed, unidirectional, back-reflection-free light propagation has been demonstrated in a microwave quantum Hall system with broken time-reversal symmetry using a gyromagnetic PhC [6].”
- Topological Photonic Quasicrystals: Fractal Topological Spectrum and Protected Transport (2016, methodology): “Chronologically, the photonic equivalent of the quantum Hall effect was predicted [9,23] and observed first among the photonic topological systems in 2D [9] (using a similar technique, topological effects were also observed in 3D systems [24,25]).”
- Driven-dissipative preparation of entangled states in cascaded quantum-optical networks (2011, background): “While such a scenario is reminiscent of edge modes in quantum Hall systems [24, 25, 26, 27, 28], various artificial and more controlled realizations based on (integrated) non-reciprocal devices for optical [29, 30] and microwave [31, 32] photons are currently developed.”