Photonic Weyl points due to broken time-reversal symmetry in magnetized semiconductor

Abstract

Weyl points are discrete locations in the three-dimensional momentum space where two bands cross linearly with each other. They serve as the monopoles of Berry curvature in the momentum space, and their existence requires breaking of either time-reversal or inversion symmetry1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16. Although various non-centrosymmetric Weyl systems have been reported15, demonstration of Weyl degeneracies due to breaking of the time-reversal symmetry remains scarce and is limited to electronic systems17,18. Here, we report the experimental observation of photonic Weyl degeneracies in a magnetized semiconductor—InSb, which behaves as a magnetized plasma19 for electromagnetic waves at the terahertz band. By varying the magnetic field strength, Weyl points and the corresponding photonic Fermi arcs have been demonstrated. Our observation establishes magnetized semiconductors as a reconfigurable20 terahertz Weyl system, which may prompt research on novel magnetic topological phenomena such as chiral Majorana-type edge states and zero modes in classic systems21,22.

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Fig. 1: Bulk states of lossless magnetized InSb.
Fig. 2: Observation of a terahertz Weyl point in a magnetized semiconductor system.
Fig. 3: Surface states under tilted-incidence excitation.
Fig. 4: Photonic Weyl points and Fermi arcs in the synthetic space.

Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

We thank Z. Zhang and C. Zhang at Capital Normal University for experimental instrument support. This work is supported by the European Research Council Consolidator Grant (TOPOLOGICAL), Horizon 2020 Action Project grant 734578 (D-SPA) and 777714 (NOCTORNO), EPSRC grant no. EP/J018473/1 and the National Science Foundation of China (grant nos. 61875150 and 61420106006). S.Z. acknowledges support from the Royal Society and the Wolfson Foundation. M.N.-C. acknowledges support from the University of Birmingham (Birmingham Fellowship), the EPSRC (grant no. EP/S018395/1) and the Royal Society (grant no. IES/R3/183131).

Author information

D.W., B.Y. and S.Z. initiated the project and designed the experiment. D.W., Q.Y., X.C., M.W. and J.H. fabricated samples. D.W. and J.H. carried out the measurements. D.W., B.Y., J.H., W.Z. and S.Z. analysed data. D.W., B.Y., W.G., H.J., M.N.-C. and C.L. performed simulations. D.W., B.Y., W.G., M.N.-C., J.H., W.Z. and S.Z. provided the theoretical explanations. J.H., W.Z. and S.Z. supervised the project. All authors discussed the results and contributed to the final manuscript.

Correspondence to Jiaguang Han or Weili Zhang or Shuang Zhang.

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The authors declare no competing interests.

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Peer review information: Nature Physics thanks Francesco Monticone, Giacomo Scalari and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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