Tunable magnetism and band structure in kagome materials RETi3Bi4 family with weak interlayer interactions

Kagome lattice is compoed of a network of corner-sharing triangles and can host Dirac Fermions, the flat bands and the van Hove singularities. When combined with magnetism, plenty of topological phases have been realized in kagome lattice and fruitful novel properties have emerged, attracting significant attention in magnetism, topological physics and correlated physics. Although many kagome materials have been extensively studied, most of them are non-layered crystals with strong interlayer interactions. The strong interlayer interactions not only disrupt the intrinsic two-dimensional properties of the kagome lattice, but also pose technical difficulties in preparing thin-film devices, especially atomic-scale thin-film devices, thereby hindering experimental exploration of the intrinsic properties of the kagome lattice. The RV3Sb5 family (R = K, Rb, Cs) is one of the few layered kagome materials with weak interlayer coupling. However, due to the absence of magnetism in this system, research is limited to strongly correlated fields such as superconductivity and charge density waves. In summary, the discovery of two-dimensional kagome materials possessing magnetism and weak interlayer interaction would be of great significance for further exploring the physical properties of kagome lattices and exotic magnetic correlated topological properties.

In this work, the team find that the titanium based kagome materials RETi₃Bi₄ (RE = Sm, Eu, Gd) can be exfoliated into thin flakes with nanometer thickness (the thinnest flake with 5 nm contains about 4 layers) because of the weak interlayer interactions between the adjacent RE/Bi layers, paving the way for exploring atomic-scale thin-film devices of kagome materials. Taking RETi₃Bi₄ as a representative, the theoretical calculations demonstrate the weak interlayer interactions in RETi₃Bi₄. The magnetism of this family is solely provided by rare earth elements, therefore, the magnetism can be tuned with rare earth elements change. Tunable magnetism of out-of-plane ferromagnetism, out-of-plane anti-ferromagnetism and in-plane ferromagnetism are formed for RE = Eu, Gd and Sm respectively (Fig1(f)-(k)). Furthermore, the team carries out first-principles calculation to investigate the band structure of RETi₃Bi₄ by taking EuTi₃Bi₄ as the representative. The calculation reveals the typical characteristic of bands for the kagome materials containing the Dirac cone, flat bands and van Hove singularities (Fig2(a)-(c)). The angle-resolves photoemission spectroscopy (ARPES) is consistent with the calculation (Fig 2(g)). By comparing the ARPES of EuTi₃Bi₄, GdTi₃Bi₄ and SmTi₃Bi₄, the tunable band structures also can be observed with rare earth elements change, especially for the Fermi energy tuning (Fig2(g)-(i)). It is noteworthy that the Dirac points and van Hove singularities can be tuned close to the Fermi level for RE = Gd (Fig2(h)). This is of great significance for further exploring the topological properties of magnetic kagome materials, and also lays an experimental foundation for further investigating the intrinsic properties of thin-layer kagome lattice materials.

This study is led by Ms. Jingwen Guo (School of physics, Nanjing University), Dr. Liqin Zhou (Institute of Physics, Chinese Academy of Sciences) and Mr. Jianyang Ding (Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences). The corresponding authors are Dr. Fucong Fei (School of Materials Science and Intelligent Engineering, Nanjing University), Dr. Hongming Weng (Institute of Physics, Chinese Academy of Sciences) and Dr. Fengqi Song (School of physics, Nanjing University).

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See the article:

Tunable magnetism and band structure in kagome materials RETi₃Bi₄ family with weak interlayer interactions
https://doi.org/10.1016/j.scib.2024.06.036

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