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Observation of a phononic quadrupole topological insulator

Serra-Garcia, Marc and Peri, Valerio and Süsstrunk, Roman and Bilal, Osama R. and Larsen, Tom and Villanueva, Luis Guillermo and Huber, Sebastian D. (2018) Observation of a phononic quadrupole topological insulator. Nature, 555 (7696). pp. 342-345. ISSN 0028-0836.

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The modern theory of charge polarization in solids is based on a generalization of Berry’s phase. The possibility of the quantization of this phase arising from parallel transport in momentum space is essential to our understanding of systems with topological band structures. Although based on the concept of charge polarization, this same theory can also be used to characterize the Bloch bands of neutral bosonic systems such as photonic or phononic crystals. The theory of this quantized polarization has recently been extended from the dipole moment to higher multipole moments. In particular, a two-dimensional quantized quadrupole insulator is predicted to have gapped yet topological one-dimensional edge modes, which stabilize zero-dimensional in-gap corner states. However, such a state of matter has not previously been observed experimentally. Here we report measurements of a phononic quadrupole topological insulator. We experimentally characterize the bulk, edge and corner physics of a mechanical metamaterial (a material with tailored mechanical properties) and find the predicted gapped edge and in-gap corner states. We corroborate our findings by comparing the mechanical properties of a topologically non-trivial system to samples in other phases that are predicted by the quadrupole theory. These topological corner states are an important stepping stone to the experimental realization of topologically protected wave guides in higher dimensions, and thereby open up a new path for the design of metamaterials.

Item Type:Article
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URLURL TypeDescription ReadCube access Paper
Bilal, Osama R.0000-0003-3803-5084
Huber, Sebastian D.0000-0003-3558-351X
Additional Information:© 2018 Macmillan Publishers Limited, part of Springer Nature. Received: 15 July 2017; Accepted: 08 November 2017; Published online: 15 January 2018. We acknowledge financial support from the Swiss National Science Foundation and the NCCR QSIT. T.L. acknowledges support from a Marie Curie fellowship and O.R.B. from the ETH postdoctoral fellowship FEL-26 15-2. Data availability: The data that support the findings of this study are available from the corresponding author on reasonable request. Author Contributions: S.D.H. conceived the research. M.S.-G., V.P. and O.R.B. designed the samples. M.S.-G., V.P., S.D.H. and R.S. conducted the experiments. L.G.V. and T.L. fabricated the samples. The authors declare no competing financial interests.
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)UNSPECIFIED
Marie Curie FellowshipUNSPECIFIED
ETH ZurichFEL-26 15-2
Issue or Number:7696
Record Number:CaltechAUTHORS:20180122-111821808
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84455
Deposited By: Tony Diaz
Deposited On:23 Jan 2018 13:25
Last Modified:14 Apr 2020 21:37

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