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A quantized microwave quadrupole insulator with topologically protected corner states
Open accessAbstract
The theory of electric polarization in crystals defines the dipole moment of an insulator in terms of a Berry phase (geometric phase) associated with its electronic ground state. This concept not only solves the long-standing puzzle of how to calculate dipole moments in crystals, but also explains topological band structures in insulators and superconductors, including the quantum anomalous Hall insulator and the quantum spin Hall insulator, as well as quantized adiabatic pumping processes. A recent theoretical study has extended the Berry phase framework to also account for higher electric multipole moments, revealing the existence of higher-order topological phases that have not previously been observed. Here we demonstrate experimentally a member of this predicted class of materials—a quantized quadrupole topological insulator—produced using a gigahertz-frequency reconfigurable microwave circuit. We confirm the non-trivial topological phase using spectroscopic measurements and by identifying corner states that result from the bulk topology. In addition, we test the critical prediction that these corner states are protected by the topology of the bulk, and are not due to surface artefacts, by deforming the edges of the crystal lattice from the topological to the trivial regime. Our results provide conclusive evidence of a unique form of robustness against disorder and deformation, which is characteristic of higher-order topological insulators.
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Cited by
Topolectrical-circuit realization of topological corner modes
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Observation of a phononic quadrupole topological insulator
Serra-Garcia, M., Peri, V., Süsstrunk, R., Bilal, O. R., Larsen, T., Villanueva, L. G., & Huber, S. D. (2018) · Nature · doi:10.1038/nature25156 · Cited by 982
Higher-order topology in bismuth
Schindler, F., Wang, Z., Vergniory, M. G., Cook, A. M., Murani, A., Sengupta, S., Kasumov, A. Y., Deblock, R., Jeon, S., Drozdov, I., et al. (2018) · Nature Physics · doi:10.1038/s41567-018-0224-7 · Cited by 837
Xie, B.-Y., Su, G.-X., Wang, H.-F., Su, H., Shen, X.-P., Zhan, P., Lu, M.-H., Wang, Z.-L., & Chen, Y.-F. (2019) · Physical Review Letters · doi:10.1103/physrevlett.122.233903 · Cited by 594
Higher-order topological insulators and superconductors protected by inversion symmetry
Khalaf, E. (2018) · Physical Review B · doi:10.1103/physrevb.97.205136 · Cited by 528
Metadata
- Authors
- Peterson, C. W., Benalcazar, W. A., Hughes, T. L., & Bahl, G.
- Venue
- Nature
- Published
- 2018-03-15
- Volume
- 555
- Issue
- 7696
- Pages
- 346-350
- ISSN
- 0028-0836 (ISSN-L)
- 1476-4687
- OpenAlex
- W2761412195
- Cited by
- 818
- References
- 10
- FWCI
- 45.57
- Type
- journal article
- Language
- en
- Open access
- green
- Licence
- www.springer.com/tdm (tdm)
- www.springer.com/tdm (vor)
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