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

• Published in: Nature physics Vol. 15; no. 5; pp. 443 - 448
• Main Authors: Yin, Jia-Xin, Zhang, Songtian S., Chang, Guoqing, Wang, Qi, Tsirkin, Stepan S., Guguchia, Zurab, Lian, Biao, Zhou, Huibin, Jiang, Kun, Belopolski, Ilya, Shumiya, Nana, Multer, Daniel, Litskevich, Maksim, Cochran, Tyler A., Lin, Hsin, Wang, Ziqiang, Neupert, Titus, Jia, Shuang, Lei, Hechang, Hasan, M. Zahid
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-05-2019; Nature Publishing Group; Nature Publishing Group (NPG)
• Subjects: 639/301/1034/1038; 639/766/119; 639/766/119/2792; Atomic; Classical and Continuum Physics; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Complex Systems; Condensed Matter Physics; Curvature; Electron spin; Electron states; Electronic systems; Letter; Magnetic fields; Magnetism; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-019-0426-7

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
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–
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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.
The authors show that a magnetic material with kagome lattice planes hosts a flat band near the Fermi level. Electrons in this band exhibit ‘negative magnetism’ due to the Berry curvature.