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

Abstract

Kagome-lattices of 3d-transition metals hosting Weyl/Dirac fermions and topological flat bands exhibit non-trivial topological characters and novel quantum phases, such as the anomalous Hall effect and fractional quantum Hall effect. With consideration of spin–orbit coupling and electron correlation, several instabilities could be induced. The typical characters of the electronic structure of a 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 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, which is predicted by spin-polarized theoretical calculations, 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 near EF are observed. These multi-sets of kagome features are of orbital-selective origin and 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.

Study of the electronic properties of topological kagome metals YV$_6$Sn$_6$ and GdV$_6$Sn$_6$

“…Due to this chemical diversity, 166 materials host a wide variety of functionalities, particularly among those with magnetic host lattices. Examples include the existence of spin polarized Dirac cones in YMn 6 Sn 6 [14]; large anomalous hall effects in LiMn 6 Sn 6 * stephendwilson@ucsb.edu † These two authors contributed equally [15], GdMn 6 Sn 6 [16]; Chern topological magnetism in TbMn 6 Sn 6 [17]; competing magnetic phases in YMn 6 Sn 6 [18]; catalytic properties in MgCo 6 Ge 6 [19]; negative magnetoreistance in YMn 6 Sn 6−x Ga x [20]; and a cycloidal spin structure in HoMn 6−x Cr x Ge 6 [21].…”

Controllable spin filtering and half metallicity in $β_{12}$-borophene nanoribbons

“…As shown in Figs, 2(b) and 2(c), near the Fermi energy (E = 0), there are a flat and a quasi-flat bands for nanoribbons with AA and BB edges, respectively. These bands may reveal the novel quantum and topological phases similar to topological kagome magnet [45]. Indeed, recent studies show that the flat band with non-zero group velocity and the massive Dirac fermion near Fermi energy originates from the band with intrinsic Berry curvature [46].…”

Interplay between magnetism and band topology in Kagome magnets $R$Mn$_6$Sn$_6$

“…On the other hand, it is unclear whether the plain DFT treatment of Mn sublattice in RMn 6 Sn 6 is sufficient. Indeed, for example, a sizable Hubbard U = 4 eV had been applied on Mn-3d orbitals in DFT+DMFT to describe the measured band structure in YMn 6 Sn 6 [9], while most of other studies treated Mn within DFT [1]. Applying additional electron repulsion on Mn-3d orbitals affects their energistics-the position of the corresponding bands and DCs.…”

“…The rare-earth Tb atoms, possessing a strong easy-axis magnetocrystalline anisotropy (MA), * liqinke@ameslab.gov antiferromagnetically couple with the Mn atoms and align the Mn spins along the out-of-plane direction below the spin-reorientation temperatures T SR . This discovery of quantum-limit Chern topological magnetism in TbMn 6 Sn 6 has rekindled the interest in the RMn 6 Sn 6 family of compounds, where different R atoms and correspondingly a variety of magnetic structures provide a rich platform to explore quantum phenomena [5][6][7][8][9][10][11][12][13][14].…”