The arrangement of atoms within a material fundamentally dictates electron behavior and the resulting electronic states. Kagome lattices, characterized by repeating patterns of corner-sharing triangles with hexagonal spaces between them, are theoretically linked to the emergence of unusual electronic properties. While these structures have been extensively studied in theory, most existing kagome materials are three-dimensional, where interactions between layers often obscure the underlying physics.
A team led by Mingu Kang from Seoul National University and the Center for Complex Phase of Materials has now realized an ideal single-layer kagome system, termed "kagomene." Published in Nature Physics, their research details a new van der Waals material with the chemical formula A2T3X4. This ultrathin material allows researchers to isolate flat electronic bands, where electrons behave as if they have an extremely large effective mass, within a single atomic layer.
To identify this material, the researchers conducted a systematic high-throughput screening of a database containing approximately 183,000 materials. They identified roughly 5,300 candidates with kagome lattice structures and further filtered them to find those held together by weak forces suitable for mechanical exfoliation. After performing density functional theory calculations and synthesizing the most promising candidates, they successfully produced atomically thin layers.
Using nano-ARPES, a technique that measures electrons released by a focused light beam, the team mapped the electron states in these samples. They confirmed the presence of flat band electronic states near the Fermi level. Kang noted that this 2D kagome-based system achieves a flat band electron density more than two orders of magnitude higher than existing moiré superlattice-based systems. This significant increase is attributed to the fact that the flat band state arises intrinsically from the unique lattice geometry rather than relying on artificial, large superlattices.
The discovery provides a promising platform for exploring exotic quantum phenomena, including unconventional superconductivity and fractional quantum states. Many-body calculations suggest that the fractional quantum anomalous Hall effect in this 2D kagome lattice could emerge at energy or temperature scales an order of magnitude higher than those observed in current moiré superlattices. Specifically, the predicted scale is between 14 and 29 meV, compared to 1–5 meV in existing platforms.
Looking ahead, the team plans to develop electrically tunable devices based on these 2D kagome lattices. They aim to investigate whether strong electron interactions within the flat band can generate new quantum states such as magnetism or fractional topological states at much higher temperatures. This first genuine 2D kagome platform also opens new research directions, including the fabrication of van der Waals heterostructures and moiré superstructures based on these lattices.
Sources: Phys.org.