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Negative flat band magnetism in a spin–orbit-coupled correlated kagome magnet

  • Author(s): Yin, JX
  • Zhang, SS
  • Chang, G
  • Wang, Q
  • Tsirkin, SS
  • Guguchia, Z
  • Lian, B
  • Zhou, H
  • Jiang, K
  • Belopolski, I
  • Shumiya, N
  • Multer, D
  • Litskevich, M
  • Cochran, TA
  • Lin, H
  • Wang, Z
  • Neupert, T
  • Jia, S
  • Lei, H
  • Hasan, MZ
  • et al.
Abstract

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Electronic systems with flat bands are predicted to be a fertile ground for hosting emergent phenomena including unconventional magnetism and superconductivity 1–15 , but materials that manifest this feature are rare. Here, we use scanning tunnelling microscopy to elucidate the atomically resolved electronic states and their magnetic response in the kagome magnet Co 3 Sn 2 S 2 (refs. 16–20 ). We observe a pronounced peak at the Fermi level, which we identify as arising from the kinetically frustrated kagome flat band. On increasing the magnetic field up to ±8 T, this state exhibits an anomalous magnetization-polarized many-body Zeeman shift, dominated by an orbital moment that is opposite to the field direction. Such negative magnetism is induced by spin–orbit-coupling quantum phase effects 21–25 tied to non-trivial flat band systems. We image the flat band peak, resolve the associated negative magnetism and provide its connection to the Berry curvature field, showing that Co 3 Sn 2 S 2 is a rare example of a kagome magnet where the low-energy physics can be dominated by the spin–orbit-coupled flat band.

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