Evidence of two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn

Abstract

The kagome lattice has long been regarded as a theoretical framework that connects lattice geometry to unusual singularities in electronic structure. Transition metal kagome compounds have been recently identified as a promising material platform to investigate the long-sought electronic flat band. Here we report the signature of a two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn by means of planar tunneling spectroscopy. Employing a Schottky heterointerface of FeSn and an n-type semiconductor Nb-doped SrTiO3, we observe an anomalous enhancement in tunneling conductance within a finite energy range of FeSn. Our first-principles calculations show this is consistent with a spin-polarized flat band localized at the ferromagnetic kagome layer at the Schottky interface. The spectroscopic capability to characterize the electronic structure of a kagome compound at a thin film heterointerface will provide a unique opportunity to probe flat band induced phenomena in an energy-resolved fashion with simultaneous electrical tuning of its properties. Furthermore, the exotic surface state discussed herein is expected to manifest as peculiar spin-orbit torque signals in heterostructure-based spintronic devices.

LaIr3Ga2: A Superconductor Based on a Kagome Lattice of Ir

“…Kagome lattice materials, made from corner-sharing triangles of magnetic atoms, have attracted much attention in recent years. In addition to geometric magnetic frustration, the Kagome lattice structural motif can exhibit forefront quantum physics, such as the quantum spin liquid (QSL) state, − topological quantum state, − and superconductivity. − Exotic features in electronic structures, such as flat bands, Dirac cones, and topologically nontrivial surface states are predicted and known for Kagome lattice materials, ,,,− while insulating Kagome lattice compounds are well-known frustrated magnets, such as SrCr 12– x Ga x O 19 (SCGO) and the QSL candidate ZnCu 3 (OH)­Cl 2 . − In recent years, nontrivial electronic states in conducting Kagome-based systems have been explored in materials such as Fe 3 Sn 2 , Co 3 Sn 2 S 2 , and TbMn 6 Sn 6 . Directly related to this work, a novel family of layered materials based on a Kagome lattice of the light element vanadium, AV 3 Sb 5 (A = K, Rb, and Cs), has recently been found to host suprconductivity ( T c = 0.93, 0.92 and 2.5 K for the K, Rb, and Cs variants, respectively). ,, One of the members of this family, KV 3 Sb 5 , was found to be a topological metal, and a giant anomalous Hall effect was observed at low temperature .…”

Intrinsic anomalous Hall effect in thin films of topological kagome ferromagnet Fe3Sn2

“…[14][15][16] Two interesting families of kagome metal are 3d transition metal stannides and germannides with the general formula T m X n (here T is 3d transition metal atoms Mn, Fe, Co; and X is the space-filling atoms, Sn or Ge; and the ratio m : n = 3 : 1, 3 : 2, 1 : 1) is formed by stacking various sequences of T 3 X kagome and X 2 spacer layers. [17][18][19] Lately the FeSn-family (Fe 3 Sn, Fe 3 Sn 2 , FeSn, FeSn 2 , and Fe 5 Sn 3 ) has been investigated extensively due to the rare coexistence of Dirac fermions and flat bands in these systems. 18,[20][21][22][23][24] The crystal structure of these materials is described by different stacking of the Fe 3 Sn kagome layer and stanene (Sn 2 ) layer.…”

“…14–16 Two interesting families of kagome metal are 3d transition metal stannides and germannides with the general formula T m X n (here T is 3d transition metal atoms Mn, Fe, Co; and X is the space-filling atoms, Sn or Ge; and the ratio m : n = 3 : 1, 3 : 2, 1 : 1) is formed by stacking various sequences of T 3 X kagome and X 2 spacer layers. 17–19…”

Pressure-induced superconductivity in flat-band Kagome compounds Pd$_3$P$_2$(S$_{1-x}$Se$_x$)$_8$

“…Kagome lattice systems have been proposed to host rich physics, such as quantum spin liquid and unconventional superconductivity in systems with strong electron correlations [1][2][3][4][5] . Recently, the electronic flat band [6][7][8][9][10][11][12][13][14][15] and Dirac cones [9][10][11][16][17][18][19][20][21][22] were also observed and caused intense research interests in several metallic kagome materials, where the electron correlations appear to be weak. In the Kagome lattice, the flat band arises from phase destruction of electron wave functions in the corner shared triangles, so that one electron band is localized in the hexagons 23,24 .…”

“…Unfortunately, the electron correlations in the flat-band Kagome materials seems to be too weak to offer any novel phase so far [6][7][8][9][10][11][12][13][14][15] . In parallel, signatures of flat bands and the related novel phases have been discovered experimentally in twisted bilayer graphene 30,31 , silicene 32 and dichalcogenides 33 .…”