A photonic amorphous topological isolator.

The current understanding of topological insulators and their classic wave analogs, such as photonic topological insulators, is primarily based on topological band theory. Contrary to this, scientists in China and Singapore experimentally showed photonic topological insulators based on glass-like amorphous phases, for which the band structure is poorly defined. The persistence of topological protection is also closely related to the transition from glass to liquid. This interaction between topology and amorphous opens the way for new kinds of non-crystalline topological non-photological band photological 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), the photonic analogues of electronic topological isolators, have enabled unprecedented exciting photonic functionalities such as robust one-way photonic transport and topological lasers.

These topological systems, whether based on condensed or photonic matter, generally derive their topological properties from band structures based on periodic networks. On the other hand, amorphous photonic phases without periodic atomic networks exist widely in nature (eg, glass, polymers, and gels). The properties of these amorphous systems are determined by the short-range connectivity of their atoms / molecules, rather than the long-range periodicity.

In a new article published in Light science and applications, a team of scientists led by Professor Peiheng Zhou and Professor Longjiang Deng of the China University of Electronic Science and Technology, Professor Yidong Chong and Professor Baile Zhang of Nanyang University of Technology have experimentally performed amorphous PTIs which are non-crystalline variants of a Chern PTI based on numbers. Their study demonstrates the interesting interaction between topology and short-range order, especially during the glass transition. Chern number-based PTIs are the first type of PTI ever performed. Their work is the first to study amorphous PTIs that use this type of photonic structure. They also find that the extinction of the states of the photonic topological border refers to the glass transition. These ideas can be useful for making amorphous topological insulators in other physical environments such as acoustics.

Amorphous PTI consists of gyro-magnetic rods that are arranged in computer-generated amorphous lattice patterns and magnetically polarized to break time reversal symmetry. By performing edge / volume transmission and near-field distribution measurements to PTIs on a copper parallel plate waveguide, the existence of robust topological edge states in amorphous PTIs is experimentally verified before the start of the glass transition. By further deforming the amorphous network into a liquid-type network, the closing of the mobility gap and the disappearance of the topological edge states are observed. These scientists summarize the characteristics of their topological system:

“We designed an amorphous PTI system with three advantages: (1) amorphous networks are achievable in natural materials, as they are generated by molecular dynamics methods; (2) complete mapping of crystalline to amorphous phases to liquid to liquid produces all the evaluation of the topology, from the appearance to the extinction, and clearly captures the role of the glass-liquid transition, and (3) the photonic platform can be immigrated to verify other non-periodic photonic topological materials. “

“The topological protection backed by the short-range order in our amorphous PTIs demonstrates remarkable robustness against large defects, for example 3 times the characteristic length of nets and 90 ° curves, all comparable to their crystalline counterparts,” they added.

“The approach presented can be used to develop specific amorphous ITP with desired structural correlations, eg hyperuniform structures studied in band-gap photonic crystals, or monitor other non-periodic ITP, eg quasicrystals or metamaterials. Therefore, Our findings will be very useful for future research work on non-crystalline topological photonic materials for novel photonic devices, such as topological random lasers, “the scientists propose.