Recently, topological kagome metals (TKMs) are rapidly being recognized as exciting topological (semi)metals because the electronic band structure near the Fermi energy primarily originates from d or f electrons imparting magnetic ordering and electron correlations, and there are additionally significant portions of the Brillouin zone where the energetic dispersion for electronic excitations is minimal (i.e., ‘flat band’ regions). At the heart of TKMs are layered 2D kagome lattices occupied by transition metals (Fe, Mn, Co), which give rise to Weyl/Dirac cones and flat bands.
In the case of binary TKM TmXn kagome series (T = Fe, Co, Mn; X = Sn, Ge; m:n = 3:1, 3:2, 1:1), they consist of kagome T3X layers and honeycomb X layers. In the T3X layer, T atoms form a kagome lattice with X atoms located at the hexagon center. The T3X and X layers are stacked in various ways to form T3X, T3X2, and TX, respectively, with a dimensional progression from 3D to 2D as the separation between kagome layers increases. |
Among the binary TKMs, Mn3Sn, Fe3Sn2, FeSn and CoSn exhibit many exotic properties in bulk crystals, which call for the transformation to high-quality thin films that are crucial to explore the topological surface states, to interface TKMs with other quantum materials, and to develop novel devices. For the last three years, we have realized a wide range of epitaxial TKM films with superior crystalline quality, sharp interfaces and smooth surface, as exemplified in the figure below. In addition, we have observed many unprecedented properties such as Kondo gap opening, resonance-enhanced THz Faraday rotation, large anomalous Hall/Nernst effects, unusual spin orbit torque, and potential triplet superconductivity.
Relevant publications
1. High-quality epitaxial thin films of topological kagome metal CoSn by magnetron sputtering, T. R. Thapaliya, Timothy Yoo, Sebastian Hurtado Parra, Nathan D. Arndt, R. F. Need, James M. Kikkawa, Honggyu Kim, and S. X. Huang, Applied Physics Letters 119, 201902 (2021).
2. Kondo physics in antiferromagnetic Weyl semimetal Mn3+xSn1-x films, Durga Khadka, T. R. Thapaliya, Sebastian Hurtado Parra, Xingyue Han, Jiajia Wen, Ryan F. Need, Pravin Khanal, Weigang Wang, Jiadong Zang, James M. Kikkawa, Liang Wu, and S. X. Huang*, Science Advances 6, eabc1977 (2020).
3. Anomalous Hall and Nernst effects in epitaxial films of topological kagome magnet Fe3Sn2, Durga Khadka, T. R. Thapaliya, Sebastian Hurtado Parra, Jiajia Wen, Ryan Need, James M. Kikkawa, and S. X. Huang, Physical Review Materials 4, 084203 (2020).
4. High quality epitaxial thin films and exchange bias of antiferromagnetic Dirac semimetal FeSn, Durga Khadka, T. R. Thapaliya, Jiajia Wen, Ryan F. Need, and S. X. Huang, Applied Physics Letters 117, 032403 (2020).
2. Kondo physics in antiferromagnetic Weyl semimetal Mn3+xSn1-x films, Durga Khadka, T. R. Thapaliya, Sebastian Hurtado Parra, Xingyue Han, Jiajia Wen, Ryan F. Need, Pravin Khanal, Weigang Wang, Jiadong Zang, James M. Kikkawa, Liang Wu, and S. X. Huang*, Science Advances 6, eabc1977 (2020).
3. Anomalous Hall and Nernst effects in epitaxial films of topological kagome magnet Fe3Sn2, Durga Khadka, T. R. Thapaliya, Sebastian Hurtado Parra, Jiajia Wen, Ryan Need, James M. Kikkawa, and S. X. Huang, Physical Review Materials 4, 084203 (2020).
4. High quality epitaxial thin films and exchange bias of antiferromagnetic Dirac semimetal FeSn, Durga Khadka, T. R. Thapaliya, Jiajia Wen, Ryan F. Need, and S. X. Huang, Applied Physics Letters 117, 032403 (2020).