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  Quasi-symmetry-protected topology in a semi-metal

Guo, C., Hu, L., Putzke, C., Diaz, J., Huang, X., Manna, K., et al. (2022). Quasi-symmetry-protected topology in a semi-metal. Nature Physics, 1-7. doi:10.1038/s41567-022-01604-0.

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 Creators:
Guo, Chunyu1, Author
Hu, Lunhui1, Author
Putzke, Carsten1, Author
Diaz, Jonas1, Author
Huang, Xiangwei1, Author
Manna, Kaustuv2, Author           
Fan, Feng-Ren2, Author           
Shekhar, Chandra3, Author           
Sun, Yan2, Author           
Felser, Claudia4, Author           
Liu, Chaoxing1, Author
Bernevig, B. Andrei1, Author
Moll, Philip J. W.1, Author
Affiliations:
1external, ou_persistent22              
2Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863425              
3Chandra Shekhar, Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863428              
4Claudia Felser, Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863429              

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 Abstract: The concept of quasi-symmetry-a perturbatively small deviation from exact symmetry-is introduced and leads to topological materials with strong resilience to perturbations. The crystal symmetry of a material dictates the type of topological band structure it may host, and therefore, symmetry is the guiding principle to find topological materials. Here we introduce an alternative guiding principle, which we call 'quasi-symmetry'. This is the situation where a Hamiltonian has exact symmetry at a lower order that is broken by higher-order perturbation terms. This enforces finite but parametrically small gaps at some low-symmetry points in momentum space. Untethered from the restraints of symmetry, quasi-symmetries eliminate the need for fine tuning as they enforce that sources of large Berry curvature occur at arbitrary chemical potentials. We demonstrate that quasi-symmetry in the semi-metal CoSi stabilizes gaps below 2 meV over a large near-degenerate plane that can be measured in the quantum oscillation spectrum. The application of in-plane strain breaks the crystal symmetry and gaps the degenerate point, observable by new magnetic breakdown orbits. The quasi-symmetry, however, does not depend on spatial symmetries and hence transmission remains fully coherent. These results demonstrate a class of topological materials with increased resilience to perturbations such as strain-induced crystalline symmetry breaking, which may lead to robust topological applications as well as unexpected topology beyond the usual space group classifications.

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Language(s): eng - English
 Dates: 2022-05-162022-05-16
 Publication Status: Published in print
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Title: Nature Physics
  Other : Nat. Phys.
Source Genre: Journal
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Publ. Info: London : Nature Pub. Group
Pages: - Volume / Issue: - Sequence Number: - Start / End Page: 1 - 7 Identifier: ISSN: 1745-2473
CoNE: https://pure.mpg.de/cone/journals/resource/1000000000025850