Discovery of topological Weyl fermion lines and drumhead surface states in a room temperature magnet
Magnetic Weyl semimetals
Weyl semimetals (WSMs)—materials that host exotic quasiparticles called Weyl fermions—must break either spatial inversion or time-reversal symmetry. A number of WSMs that break inversion symmetry have been identified, but showing unambiguously that a material is a time-reversal-breaking WSM is tricky. Three groups now provide spectroscopic evidence for this latter state in magnetic materials (see the Perspective by da Silva Neto). Belopolski et al. probed the material Co2MnGa using angle-resolved photoemission spectroscopy, revealing exotic drumhead surface states. Using the same technique, Liu et al. studied the material Co3Sn2S2, which was complemented by the scanning tunneling spectroscopy measurements of Morali et al. These magnetic WSM states provide an ideal setting for exotic transport effects.
Abstract
Topological matter is known to exhibit unconventional surface states and anomalous transport owing to unusual bulk electronic topology. In this study, we use photoemission spectroscopy and quantum transport to elucidate the topology of the room temperature magnet Co2MnGa. We observe sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase. On the surface of the magnet, we observe electronic wave functions that take the form of drumheads, enabling us to directly visualize the crucial components of the bulk-boundary topological correspondence. By considering the Berry curvature field associated with the observed topological Weyl fermion lines, we quantitatively account for the giant anomalous Hall response observed in this magnet. Our experimental results suggest a rich interplay of strongly interacting electrons and topology in quantum matter.
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Science
Volume 365 | Issue 6459
20 September 2019
20 September 2019
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Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
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Submission history
Received: 29 August 2018
Accepted: 14 August 2019
Published in print: 20 September 2019
Acknowledgments
We thank D. Lu and M. Hashimoto at Beamlines 5-2 and 5-4 of the Stanford Synchrotron Radiation Lightsource (SSRL) at the SLAC National Accelerator Laboratory, CA, USA, and J. Denlinger at Beamline 4.0.3 and S.-K. Mo at Beamline 10.0.1 of the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory (LBNL), CA, USA, for support. Funding: Work at Princeton University is supported by the U.S. Department of Energy (DOE) under Basic Energy Sciences, grant no. DOE/BES DE-FG-02-05ER46200. I.B. acknowledges the support of the Harold W. Dodds Fellowship of Princeton University. The work at Northeastern University was supported by DOE, Office of Science, Basic Energy Sciences grant no. DE-FG02-07ER46352 and benefited from Northeastern University’s Advanced Scientific Computation Center (ASCC) and the NERSC supercomputing center through DOE grant no. DE-AC02-05CH11231. Use of the Stanford Synchrotron Radiation Lightsource (SSRL), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-76SF00515. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. K.M., B.E., and C.F. acknowledge the financial support by the ERC Advanced Grant no. 291472 “Idea Heusler” and 742068 “TOPMAT.” STM characterization of samples was supported by the Gordon and Betty Moore Foundation (GBMF4547/Hasan). M.Z.H. acknowledges support from the Miller Institute of Basic Research in Science at the University of California at Berkeley and Lawrence Berkeley National Laboratory in the form of a Visiting Miller Professorship during the early stages of this work. M.Z.H. also acknowledges visiting scientist support from IQIM at the California Institute of Technology. Author contributions: The project was initiated by I.B., K.M., C.F., and M.Z.H. I.B. and D.S.S. carried out ARPES measurements and analyzed ARPES data with assistance from G.C., J.Y., S.S.Z., T.C., N.S., H.Z., G.B., D.M., M.L., S.-Y.X., and M.Z.H. K.M. synthesized the single-crystal samples and carried out the transport and magnetization measurements with assistance from B.E. I.B. and K.M. analyzed the transport data with assistance from G.C. and T.C. G.C. performed first-principles calculations and theoretical analysis with assistance and guidance from B.S., G.B., X.Z., S.-M.H., B.W., T.-R.C., S.-Y.X., A.B., and H.L. The project was supervised by C.F., H.L., and M.Z.H. All authors discussed the results and contributed to writing the manuscript. Competing interests: The authors declare no competing interests. Data and materials availability: The data presented in this work are available on Zenodo (34).
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