The current understanding of topological insulators and their classical wave analogs, such as photonic topological insulators, is based mainly on the theory of topological bands. In contrast, scientists in China and Singapore have experimentally demonstrated photonic topological isolators based on glassy amorphous phases for which no bandage is defined. It has also been found that the persistence of topological protection is closely related to the transition from glass to fluid. This interplay between topology and amorphous prepares the ground for new classes of non-crystalline topological photonic bandgap materials.
The concept of paradigm shift topology has not only revolutionized condensed matter physics, but has also opened a fundamentally new chapter in photonics, mechanics, acoustics and many other fields. In photonics, “photonic topological isolators” (PTIs), photonic analogs of electronic topological isolators, have enabled unprecedented exciting photonic functions, such as one-way robust photonic transport and topological lasers.
These topological systems, whether based on condensed matter or photonics, usually derive their topological properties from bandstructures based on periodic lattices. On the other hand, photonic amorphous phases without periodic atomic lattices (eg glass, polymers and gels) widely exist in nature. The properties of these amorphous systems are determined by the connectivity of their atoms / molecules of short range rather than by long-term periodicity.
In a new document published in Light Science & Applications, a team of scientists led by Professor Peiheng Zhou and Professor Longjiang Deng of the University of Electronic Sciences and Technology in China, Professor Yidong Chong and Professor Baile Zhang of Nanyang University of Technology experimentally implemented amorphous PTIs, which are non-crystalline variants of Black-Number PTI. Their study demonstrates an interesting interplay between topology and short order, especially during the transition to glass. Number-based PTIs are the first type of PTI ever implemented. Their work is the first to study amorphous PTI using this type of photonic structure. They also found that the extinction of photonic topological boundary states involves the glass transition. This knowledge may be useful in implementing amorphous topological insulators in other physical environments, such as acoustics.
Amorphous PTI consists of gyromagnetic rods that are arranged in computer-generated amorphous grating patterns and magnetically affected to break the time-reverse symmetry. By measuring edge / volume transfer and near-field distribution to PTI in a copper parallel waveguide, the existence of robust topological edge states in amorphous PTIs before the start of the glass transition is experimentally verified. Further deformation of the amorphous lattice into a fluid-like lattice observes the closing of the mobility gap and the disappearance of the topological boundary states. These scientists summarize the features of their topological system:
“We have designed an amorphous PTI system with three advantages: (1) amorphous lattices are feasible in natural materials because they are generated by molecular dynamics methods; (2) provides a complete mapping from crystalline amorphous amorphous to liquid phases for an overall topology assessment from onset to extinction and clearly captures the role of the glass-liquid transition; and (3) the photonic platform can be migrated to verify other non-periodic photonic topological materials. ‘ “
“The topological protection supported by the short-term order in our amorphous PTIs shows exceptional resistance to large defects, such as three times the characteristic length of grids and 90 ° bends, all comparable to crystalline counterparts,” they added.
“The present approach can be used to develop specific amorphous PTIs with the desired structural correlations, e.g. Hyperuniform structures studied on bandgap photonic crystals or monitoring of other non-periodic PTIs, for example quasi-crystals or metamaterials. Our findings will therefore be very useful. for future work investigating non-crystalline topological photonic materials for new photonic devices, such as topological random lasers, ”the scientists suggest.
Topological photonics in fractal gratings
Peiheng Zhou et al., Photonic amorphous topological isolator, Light: Science and applications (2020). DOI: 10,1038 / s41377-020-00368-7
Provided by the Chinese Academy of Sciences
Citations: Photonic amorphous topological isolator (2020, July 27) obtained on July 29, 2020 from https://phys.org/news/2020-07-photonic-amorphous-topological-insulator.html
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