Spin excitations in metallic kagome lattice FeSn and CoSn

Abstract

In two-dimensional (2D) metallic kagome lattice materials, destructive interference of electronic hopping pathways around the kagome bracket can produce nearly localized electrons, and thus electronic bands that are flat in momentum space. When ferromagnetic order breaks the degeneracy of the electronic bands and splits them into the spin-up majority and spin-down minority electronic bands, quasiparticle excitations between the spin-up and spin-down flat bands should form a narrow localized spin-excitation Stoner continuum coexisting with well-defined spin waves in the long wavelengths. Here we report inelastic neutron scattering studies of spin excitations in 2D metallic kagome lattice antiferromagnetic FeSn and paramagnetic CoSn, where angle resolved photoemission spectroscopy experiments found spin-polarized and nonpolarized flat bands, respectively, below the Fermi level. Our measurements on FeSn and CoSn reveal well-defined spin waves extending above 140 meV and correlated paramagnetic scattering around Γ point below 90 meV, respectively. In addition, we observed non-dispersive excitations at ~170 meV and ~360 meV arising mostly from hydrocarbon scattering of the CYTOP-M used to glue the samples to aluminum holder. Therefore, our results established the evolution of spin excitations in FeSn and CoSn, and identified anomalous flat modes overlooked by the neutron scattering community for many years.

Electron-Correlation-Induced Charge Density Wave in FeGe

“…[80] The band structure and DOS (see the SMs) are basically similar in many aspects to the isostructure FeSn. [58][59][60][61][62] Our calculations reproduce the results of previous studies [65] quite well. The magnetic moment of the Fe ions is estimated to be 1.55𝜇B, which is close to the previous experimental value of about 1.72𝜇B.…”

“…[35][36][37] In this system, vHSs are located near the Fermi level and the phonon spectrum exhibits two imaginary phonon frequencies locating at the Brillouin zone (BZ) boundary [𝑀 ( 12 , 0, 0) and 𝐿 ( 1 2 , 0, 1 2 ) points], [29,30] which induce an in-plane 2×2 CDW state identified in experiment. [21][22][23][24][25][26] On the other hand, there are many kagome magnetic materials such as FeSn, [58][59][60][61][62] Fe3Sn2, [63,64] Mn3Sn, [14] Mn3Ge, [50,54] and Co3Sn2S2. [15][16][17] However, it may be due to the large energy separation between flat bands and vHSs that CDW order and magnetic order have not been generally observed simultaneously in one material.…”

Chiral and flat-band magnetic quasiparticles in ferromagnetic and metallic kagome layers

“…However, the strong damping observed at low temperatures and high energies (above the phonon cutoff) would be inconsistent with these mechanisms. Rather, the damping observed in TbMn 6 Sn 6 and other FM kagome metals, such as YMn 6 Sn 6 24 and FeSn 25 – 27 , is more consistent with the Landau damping caused by the decay of magnons into particle-hole excitations (Stoner excitations). Recent ab initio calculations for FeSn are consistent with heavy Landau damping for magnons above 80 meV 50 .…”

$T_{3}$Pb$_{2}Ch_{2}$ ($T$=Pd,Pt and $Ch$=S,Se) with transition metal kagome net: Dynamical properties, phonon nodal line, phonon surface states, and chiral phonons

“…For example, recently discovered systems AV 3 Sb 5 (A=K, Rb, Cs) [16] with vanadium kagome lattice, are characterized by the coexistence of superconductivity and charge density waves at low temperatures [17]. Magnetic systems containing the kagome lattice [18] exhibit Weyl behavior, which has been observed, for example, in the magnetic Mn 3 Sn [19], FeSn [20][21][22], CoSn [3,[21][22][23] Fe 3 Sn 2 [24] and Co 3 Sn 2 S 2 [25]. Typically, such compounds are also characterized by an intrinsic anomalous Hall effect [26][27][28][29][30][31].…”