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.
| Original language | English |
|---|---|
| Article number | 240 |
| Journal | Communications Physics |
| Volume | 4 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 2021 |
Funding
We wish to express our sincere appreciation to the referees involved in the peer review of this paper, including those involved during the initial submission of our article to another journal in the Nature Portfolio. In particular, we would like to thank reviewer #2 at that journal, as their informative report inspired us to carry measurements on CoSn, revealing the initial misinterpretations of the data and yielding the results presented now in the published article. The neutron scattering and FeSn/CoSn materials synthesis work at Rice was supported by US DOE-DE-SC0012311 and by the Robert A. Welch Foundation under Grant No. C-1839 (P.D.), respectively. Z.P.Y. was supported by the NSFC (Grant No. 11674030), the Fundamental Research Funds for the Central Universities (Grant No. 310421113), the National Key Research and Development Program of China grant 2016YFA0302300. The calculations used high performance computing clusters at BNU in Zhuhai and the National Supercomputer Center in Guangzhou. H.L. was supported by the National Key R&D Program of China (Grants No. 2018YFE0202600, 2016YFA0300504), the National Natural Science Foundation of China (No. 11774423, 11822412), the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (RUC) (18XNLG14, 19XNLG17). A.H.M. was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award # DE‐SC0019481, and by the Welch Foundation under award TBF1473. E.F. and H.C. acknowledge the support of U.S. DOE BES Early Career Award KC0402010 under contract DE-AC05-00OR22725.
| Funders | Funder number |
|---|---|
| U.S. DOE BES | DE-AC05-00OR22725, KC0402010 |
| U.S. Department of Energy | |
| Welch Foundation | C-1839, TBF1473 |
| Office of Science | |
| Basic Energy Sciences | DE‐SC0019481 |
| National Natural Science Foundation of China | 11774423, 11674030, 11822412 |
| Renmin University of China | 18XNLG14, 19XNLG17 |
| National Key Research and Development Program of China | 2016YFA0302300, 2016YFA0300504, 2018YFE0202600 |
| Fundamental Research Funds for the Central Universities | 310421113 |