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Axial-field-induced chiral channels in an acoustic Weyl system

Abstract

Condensed-matter and other engineered systems, such as cold atoms1, photonic2 or phononic metamaterials3, have proved to be versatile platforms for the observation of low-energy counterparts of elementary particles from relativistic field theories. These include the celebrated Majorana modes4, as well as Dirac5,6 and Weyl fermions7,8,9. An intriguing feature of the Weyl equation10 is the chiral symmetry, where the two chiral sectors have an independent gauge freedom. Although this freedom leads to a quantum anomaly11,12,13,14,15, there is no corresponding axial background field coupling differently to opposite chiralities in quantum electrodynamics. Here, we provide the experimental characterization of the effect of such an axial field in an acoustic metamaterial. We implement the axial field through an inhomogeneous potential16 and observe the induced chiral Landau levels. From the metamaterials perspective these chiral channels open the possibility for the observation of non-local Weyl orbits17 and might enable unidirectional bulk transport in a time-reversal-invariant system18.

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Fig. 1: Inhomogeneous WP separation and axial magnetic fields.
Fig. 2: Observation of chiral Landau levels.
Fig. 3: Characterization of surface Fermi arcs.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We acknowledge insightful discussions with D. Pikulin and A. Stern. We are grateful for financial support from the Swiss National Science Foundation, the NCCR QSIT. This work has received funding from the European Research Council under grant agreement no. 771503.

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S.D.H., R.I. and V.P. performed the theoretical part of this work. M.S.-G. and V.P. conducted the experiments. All authors contributed to the writing of the manuscript.

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Correspondence to Sebastian D. Huber.

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Supplementary information

Supplementary Information

Supplementary Text, Supplementary Figures 1–8 and Supplementary References.

Supplementary Video 1

Video showing the frequency response in momentum space as a function of excitation frequency.

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Peri, V., Serra-Garcia, M., Ilan, R. et al. Axial-field-induced chiral channels in an acoustic Weyl system. Nat. Phys. 15, 357–361 (2019). https://doi.org/10.1038/s41567-019-0415-x

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