Photonic topological insulator with broken timereversal symmetry
A topological insulator is a material with an insulating interior but timereversal symmetryprotected conducting edge states. Since its prediction and discovery almost a decade ago, such a symmetryprotected topological phase has been explored beyond electronic systems in the realm of photonics. Electrons are spin1/2 particles, whereas photons are spin1 particles. The distinct spin difference between these two kinds of particles means that their corresponding symmetry is fundamentally different. It is well understood that an electronic topological insulator is protected by the electron’s spin1/2 (fermionic) timereversal symmetry T$$2\atop{f}$$ = 1. However, the same protection does not exist under normal circumstances for a photonic topological insulator, due to photon’s spin1 (bosonic) timereversal symmetry T$$2\atop{b}$$ = 1. Here, we report a design of photonic topological insulator using the Tellegen magnetoelectric coupling as the photonic pseudospin orbit interaction for left and right circularly polarized helical spin states. The Tellegen magnetoelectric coupling breaks bosonic timereversal symmetry but instead gives rise to a conserved artificial fermioniclikepseudo timereversal symmetry, T _{p} ( T$$2\atop{p}$$ = 1), due to the electromagnetic duality. Surprisingly, we find that, in this system, the helical edge states are, in fact, protected by this fermioniclike pseudo timereversal symmetry T _{p} rather than by the bosonic timereversal symmetry T _{b}. This remarkable finding is expected to pave a new path to understanding the symmetry protection mechanism for topological phases of other fundamental particles and to searching for novel implementations for topological insulators.
 Authors:

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 Nanjing Univ. (China). National Lab. of Solid State Microstructures and Dept. of Materials Science and Engineering
 Nanjing Univ. (China). Collaborative Innovation Center of Advanced Microstructures (CICAM), National Lab. of Solid State Microstructures and Dept. of Materials Science and Engineering
 Univ. of Oxford (United Kingdom). Clarendon Lab. and Dept. of Physics
 State Univ. of New York (SUNY), Buffalo, NY (United States). Dept. of Electrical Engineering
 Publication Date:
 Grant/Contract Number:
 SC0014485; 2012CB921503; 2013CB632702; 11134006; 11474158; 11404164; 187 N660011114105
 Type:
 Accepted Manuscript
 Journal Name:
 Proceedings of the National Academy of Sciences of the United States of America
 Additional Journal Information:
 Journal Volume: 113; Journal Issue: 18; Journal ID: ISSN 00278424
 Publisher:
 National Academy of Sciences, Washington, DC (United States)
 Research Org:
 State Univ. of New York (SUNY), Buffalo, NY (United States)
 Sponsoring Org:
 USDOE Office of Science (SC); National Basic Research Program of China; National Nature Science Foundation of China (NSFC); Defense Advanced Research Projects Agency (DARPA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; photonic topological insulator; piezoelectric/piezomagnetic superlattice; photonic crystal; polariton; timereversal symmetry
 OSTI Identifier:
 1469298
He, Cheng, Sun, XiaoChen, Liu, XiaoPing, Lu, MingHui, Chen, Yulin, Feng, Liang, and Chen, YanFeng. Photonic topological insulator with broken timereversal symmetry. United States: N. p.,
Web. doi:10.1073/pnas.1525502113.
He, Cheng, Sun, XiaoChen, Liu, XiaoPing, Lu, MingHui, Chen, Yulin, Feng, Liang, & Chen, YanFeng. Photonic topological insulator with broken timereversal symmetry. United States. doi:10.1073/pnas.1525502113.
He, Cheng, Sun, XiaoChen, Liu, XiaoPing, Lu, MingHui, Chen, Yulin, Feng, Liang, and Chen, YanFeng. 2016.
"Photonic topological insulator with broken timereversal symmetry". United States.
doi:10.1073/pnas.1525502113. https://www.osti.gov/servlets/purl/1469298.
@article{osti_1469298,
title = {Photonic topological insulator with broken timereversal symmetry},
author = {He, Cheng and Sun, XiaoChen and Liu, XiaoPing and Lu, MingHui and Chen, Yulin and Feng, Liang and Chen, YanFeng},
abstractNote = {A topological insulator is a material with an insulating interior but timereversal symmetryprotected conducting edge states. Since its prediction and discovery almost a decade ago, such a symmetryprotected topological phase has been explored beyond electronic systems in the realm of photonics. Electrons are spin1/2 particles, whereas photons are spin1 particles. The distinct spin difference between these two kinds of particles means that their corresponding symmetry is fundamentally different. It is well understood that an electronic topological insulator is protected by the electron’s spin1/2 (fermionic) timereversal symmetry T$2\atop{f}$ = 1. However, the same protection does not exist under normal circumstances for a photonic topological insulator, due to photon’s spin1 (bosonic) timereversal symmetry T$2\atop{b}$ = 1. Here, we report a design of photonic topological insulator using the Tellegen magnetoelectric coupling as the photonic pseudospin orbit interaction for left and right circularly polarized helical spin states. The Tellegen magnetoelectric coupling breaks bosonic timereversal symmetry but instead gives rise to a conserved artificial fermioniclikepseudo timereversal symmetry, Tp (T$2\atop{p}$ = 1), due to the electromagnetic duality. Surprisingly, we find that, in this system, the helical edge states are, in fact, protected by this fermioniclike pseudo timereversal symmetry Tp rather than by the bosonic timereversal symmetry Tb. This remarkable finding is expected to pave a new path to understanding the symmetry protection mechanism for topological phases of other fundamental particles and to searching for novel implementations for topological insulators.},
doi = {10.1073/pnas.1525502113},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 18,
volume = 113,
place = {United States},
year = {2016},
month = {4}
}