Spin-polarized Dirac cone, flat band and saddle point in kagome magnet YMn6Sn6

Abstract

Kagome-lattice of 3d-transition metals hosting Weyl/Dirac fermions and topological flat bands exhibit non-trivial topological characters and novel quantum phases, such as anomalous Hall effect and fractional quantum Hall effect. With consideration of spin-orbit coupling and electron correlation, several instabilities could be induced. The complete characters of the electronic structure of kagome lattice, i.e. the saddle point, Dirac-cone, and flat band, around the Fermi energy (EF) remain elusive in magnetic kagome materials. We present the first experimental observation of the complete features in ferromagnetic kagome layers of YMn6Sn6 helically coupled along the c-axis, by using angle-resolved photoemission spectroscopy and band structure calculations. We demonstrate a Dirac dispersion near EF arising from a spin-polarized orbital, which carries an intrinsic Berry curvature and contributes to the anomalous Hall effect in transport measurements. In addition, a flat band and a saddle point with a high density of states and with orbital-selective characters near EF are observed. These multi-orbital kagome features could cause multi-orbital magnetism. The Dirac fermion, flat band and saddle point in the vicinity of EF open an opportunity in manipulating the topological properties in magnetic materials.

Rare Earth Engineering in RMn6Sn6 ( R=Ma1, Xu2, Yin3 et al. 2021Phys. Rev. Lett.1073330View full textAdd to dashboardCite

“…This interesting observation supports the critical role of magnetic coupling in the MDF structure. On the other hand, the THE and electronic structure in YMn 6 Sn 6 which has no 4f moments, deserve further elaboration [23][24][25]. Our work highlights the material system which not only largely extends the family of quantum kagome magnets but also intrinsically contains a quantum knob for Chern phase engineering.…”

“…When R is Er and Tm, the Mn and Er=Tm sublattices are independently ordered in an AFM manner because the strength of the magnetic coupling is weak [17,18]. As there is no 4f moment in LuMn 6 Sn 6 , its magnetic structure was reported to be a flat spiral AFM [22], similar to that in YMn 6 Sn 6 [23][24][25].…”

Charge-density-wave-induced bands renormalization and energy gaps in a kagome superconductor RbV3Sb5

“…A typical kagome-lattice electronic band produced by the tight-binding model is characterized by a Dirac dispersion at the Brillouin zone (BZ) corner, a saddle point at the zone boundary, and a flat band through the BZ. The versatile quantum phenomena can be realized by tuning any of them close to the Fermi energy (E F ), such as Dirac/Weyl fermions [1][2][3][4][5][6][7][8][9][10][11][12][13], ferromagnetism [14][15][16], negative flat band magnetism [17], and topological Chern magnet [18]. Recently, superconductivity is discovered in a new family of layered kagome metals AV 3 Sb 5 (A= K, Rb, and Cs) (T c ∼0.9-2.5 K) [19][20][21][22][23], which host a Z 2 topological invariant and non-trivial topological Dirac surface states near E F [20].…”

Electronic Nature of Charge Density Wave and Electron-Phonon Coupling in Kagome Superconductor KV3Sb5

“…The CDW-related 2×2 lattice reconstruction is expected to generate electronic structure reconstruction, as illustrated in Fig.1d. However, no signature of such electronic reconstruction has been detected in the previous ARPES measurements[2,[37][38][39][40][41][42][43][44]. We have observed clear evidence of electronic structure reconstruction induced by the 2×2 CDW transition in KV 3 Sb 5 both in the measured Fermi surface and the band structure.Fig.…”