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Open Access Publications from the University of California

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.

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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