A quantized microwave quadrupole insulator with topologically protected corner states

A quantized microwave quadrupole insulator with topologically protected corner states, Published online: 14 March 2018; doi:10.1038/nature25777

The properties of many materials with topological band structures can be understood in terms of a quantization of the electric polarization. A new class of higher-order topological insulators has recently been predicted by considering a quantization of higher-order polarizations. Christopher Peterson et al. now use a metamaterial composed of coupled microwave resonators to demonstrate such a system experimentally: a quantized quadrupole topological insulator that has corner states that are protected by topology. By deforming one of the edges from the topological to the trivial regime, they show that these corner states move inward to the corners of the newly generated boundaries, confirming that they are protected by the topology of the bulk. Such demonstrations not only provide evidence of a unique form of robustness, but also show that reconfigurable microwave circuits are a promising platform for exploring exotic topological phases of matter. http://feeds.nature.com/nature/rss/current via https://www.nature.com/articles/nature25777

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