P-orbital higher-order photonics topological insulator

From mathematics to chemistry and biology to condensed matter physics and optics, topology-related phenomena are everywhere.

The concept of topology has been extended to optics, forming an emerging research field of topological photonics, which has been continuously developed and flourished in recent years. Recently, high-order topological insulators (HOTIs) have also sparked a research boom in the field of optics and photonics because they break the traditional body-edge correspondence, and are expected to bring new ideas for the development of next-generation semiconductor lasers and other optical devices. However , all current experimental studies of higher order topologies are limited to systems of low orbit ( S-orbital ) energy bands.

Orbital degrees of freedom play a key role in the study of the basic properties of condensed matter systems and novel states of matter (including orbital superflow and topological semimetals), and the introduction of orbital degrees of freedom can trigger and reveal many novel physical phenomena. Because the orbital degrees of freedom of electrons in real materials are difficult to manipulate, much research is based on artificial material systems, such as photonic crystals and ultracold atoms.

So, can synthetic optical platforms be used to achieve high-order topological insulators derived from high-orbital energy bands?

Recently, the research group led by Professor Chen Zhigang and Professor Xu Jingjun of the School of Physics of Nankai University/TEDA Institute of Applied Physics, and the research group of Hrvoje Buljan, distinguished professor of Nankai University and professor of the University of Zagreb, Croatia, reported the latest scientific research results of realizing new high-order photonic topological insulators in the field of topological photonics in the field of topological photonics.

The research results were published online on eLight under the title “Realization of photonic p?orbital higher?order topological insulators”.

The first authors include Zhang Yahui, a master’s student of Nankai University, Domenico Bongiovanni, a postdoctoral fellow, and doctoral students Wang Ziteng and Wang Xiangdong, who have been funded by national innovation training projects and participated in the research of this group during their undergraduate years at Nankai University. Collaborators include Shiqi Xia, a postdoctoral fellow in the School of Physics, Zhichan Hu, a doctoral student, Daohong, a professor, and Roberto Morandotti, a professor at the National Academy of Sciences. The relevant work was funded by the Key R&D Program of the Ministry of Science and Technology and the Key Project of the National Natural Science Foundation of China led by Nankai University.

Based on the photonic lattice platform, in the Kagome lattice with special symmetry, researchers experimentally observed the high-order topological angular state of p-orbit and nonlinear-induced angular rotation for the first time, and theoretically proposed to use the generalized winding number to characterize the topological non-trivial properties of the system, and innovatively found that the robustness of the topological angular state of p-orbit requires not only the protection of traditional generalized chiral symmetry, but also the unique orbital coupling symmetry in the p-orbital system.

This work demonstrates the organic combination of higher-order topology and orbital physics, as well as the dynamic regulation of higher-order orbital angular states by nonlinearity, which provides a new research platform for exploring topological systems with orbital degrees of freedom, and also lays the foundation for the development of topological vortex waveguides and topological lasers and other optical devices.

Figure 1: Schematic diagram of the generation and nonlinear regulation of p-orbital higher-order topological angular states in a Kagome photonic lattice. The dotted triangle marks a unit cell consisting of three daughter lattices ( A , B , and C ) , with t?, t? representing the magnitude of coupling within and between unit cells, respectively. Each lattice point corresponds to a laser-written waveguide that supports the p-orbital mode (see left inset). The illustration on the right marks two types of orbital coupling. At the top of the cage lattice, a robust p-orbital “angular zero-energy mode” is depicted, protected by generalized chiral symmetry and orbital coupling symmetry despite being driven by nonlinearity.

eLight is a sister journal of Light: Science & Applications (IF=20.257), a leading journal of the International Top Optical Journal/China’s Science and Technology Journals Excellence Program, created by Light’s original editorial team, and only publishes the top and most influential scientific research work in the field of optical intersection. Previously, the outlook review “Highlighting Photonics: Looking into the next decade” written by Nankai University Chair Professor Chen Zhigang and Technion Segev for the inaugural issue of the journal has been downloaded 14,000 times and cited more than 130 times since its publication in June 2021, and won the eLight 2022 Best Download/Citation Paper Award. (Source: China Optics WeChat public account)

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