Observation of Weyl nodes in TaAs

Abstract

In 1929, H. Weyl proposed that the massless solution of the Dirac equation represents a pair of a new type of particles, the so-called Weyl fermions1. However, their existence in particle physics remains elusive after more than eight decades. Recently, significant advances in both topological insulators and topological semimetals have provided an alternative way to realize Weyl fermions in condensed matter, as an emergent phenomenon: when two non-degenerate bands in the three-dimensional momentum space cross in the vicinity of the Fermi energy (called Weyl nodes), the low-energy excitations behave exactly as Weyl fermions. Here we report the direct observation in TaAs of the long-sought-after Weyl nodes by performing bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy measurements. The projected locations at the nodes on the (001) surface match well to the Fermi arcs, providing undisputable experimental evidence for the existence of Weyl fermionic quasiparticles in TaAs.

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Figure 1: Crystal structure and electronic structure of TaAs.
Figure 2: Core-level spectra and electronic structure in the kx = 0 plane.
Figure 3: Band dispersions near the Weyl nodes W1.
Figure 4: Band dispersions near the Weyl nodes W2.
Figure 5: Relationship between bulk Weyl nodes and surface Fermi arcs.

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Acknowledgements

We acknowledge help in plotting figures from H. Miao and W. L. Zhang. This work was supported by the Ministry of Science and Technology of China (Nos 2013CB921700, 2015CB921300, 2011CBA00108 and 2011CBA001000), the National Natural Science Foundation of China (Nos 11474340, 11422428, 11274362 and 11234014), the Chinese Academy of Sciences (No. XDB07000000), the Sino-Swiss Science and Technology Cooperation (No. IZLCZ2138954), and the Swiss National Science Foundation (No. 200021-137783).

Author information

H.D., T.Q. and M.S. conceived the experiments. B.Q.L., N.X. and J.Z.M. performed ARPES measurements with the assistance of C.E.M., F.B., V.N.S. and J.M. H.M.W., Z.F. and X.D. performed ab initio calculations. N.X., B.Q.L., J.Z.M., T.Q. and H.D. analysed the experimental data. N.X., B.Q.L. and H.M.W. plotted the figures. T.Q., H.D., H.M.W., M.S. and P.R. wrote the manuscript. X.C.H., L.X.Z. and G.F.C. synthesized the single crystals.

Correspondence to T. Qian or M. Shi or H. Ding.

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Lv, B., Xu, N., Weng, H. et al. Observation of Weyl nodes in TaAs. Nature Phys 11, 724–727 (2015). https://doi.org/10.1038/nphys3426

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