Cataloging High‐Quality Two‐Dimensional van der Waals Materials with Flat Bands

Abstract

Benefited from the lower dimensionality compared to their 3D counterpart, 2D flat‐band systems provide cleaner lattice models, easier experimental verification, and higher tunability, which make the 2D van der Waals (vdW) system an ideal playground for exploring flat‐band physics as well as their potential applications. Given the vast amount of research in the field of flat bands, a simple and efficient approach to search for realistic vdW materials with flat bands is still missing. Here, a two‐tier framework to filter and diagnose high‐quality flat‐band vdW materials by combining high‐throughput first‐principles calculations and the proposed 2D flat‐band score criterion is presented. Based on systematic geometrical analysis, 861 potential monolayer vdW materials are initially obtained amounting to 187,093 structures as stored in the Inorganic Crystal Structure Database. By applying the 2D flat‐band score criterion, 229 flat‐band candidates are efficiently identified, among which a sub‐catalog of 74 materials with flat bands right next to the Fermi level is further provided to facilitate experimental verification. All these efforts to screen experimentally available flat‐band candidates will certainly motivate continuing exploration toward the realization of this class of special materials and their applications in material science.

Layer Control of Magneto-Optical Effects and Their Quantization in Spin-Valley Splitting Antiferromagnets

“…The B (D, F) and A (C, E) layers are related to each other by an inversion symmetry (without considering magnetism). So, the ferroelectric polarization direction of B, D, and F monolayers is along the - z direction, which are revealed by recent theoretical and experimental reports. , While the magnetism of Nb 3 I 8 has yet to be measured experimentally, several preceding theoretical works have forecasted its layer-dependent magnetic properties, − e.g., ferromagnetism for monolayer and antiferromagnetism for bilayer. By comparing the total energies among the ferromagnetic, nonmagnetic, and different antiferromagnetic states (see Figures S1 and S2 and Tables S1 and S2), we find that the bulk and monolayer Nb 3 I 8 prefer to a A-type antiferromagnetic ground state (see Figure a) and ferromagnetic ground state, respectively, which is in accordance with the prior studies. − The optimized lattice constants of monolayer, bulk crystal, and bilayers are shown in Tables S1–S3, which are in reasonable agreement with the experimental results. , …”

“…The layered transition metal halides Nb 3 X 8 ( X = Cl, Br, I) have attracted increasing interest due to its exotic layered magnetic kagome lattice, topological flat bands, and transport properties. − Recently, the monolayer and few layers Nb 3 I 8 were cleaved mechanically from the bulk crystal. , There are six monolayers in the bulk Nb 3 I 8 with a stacking order of A–B–C–D–E–F along the c direction (see Figure a). Each layer hosts a breathing kagome lattice constructed by magnetic Nb trimers which are coordinated by the distorted nonmagnetic I octahedron environment, as shown in Figure (b).…”