Abstract

　　Flat bands in crystalline materials come in two kinds: atomically flat and topologically flat. Flat atomic bands are topologically trivial and commonly exist in layered materials and heavy fermion systems. Topological flat bands were recently discovered in twisted 2D materials, where the coexistence of nontrivial band topology and strong electronic correlation manifests kinds of exotic quantum phases, such as quantum anomalous Hall effect, magnetism, correlated insulating states, and superconductivity. In addition, a few 2D line-graph lattices with s orbitals were also proposed to have topological flat bands in the tight-binding approximation. Compared with the twisted superlattice, stoichiometric flat-band materials are much easier to synthesize and have a larger carrier density. Here I’ll introduce a general construction of flat bands in both 2D and 3D crystals. Using the magnetic topological quantum chemistry theory, we have a full classification of band topologies in paramagnetic and magnetic materials both with and without spin-orbit coupling. These advantages enable a complete understanding of flat-band features in most materials. By analyzing the geometry and symmetry properties, a high-throughput search and classification of topological flat-band materials were performed to build a material database.We further investigate a set of Kagome compounds and show that their flat band are the result of more convoluted properties than simple Kagome flat bands. We present a Lego-like principle to explain the existence of flat bands in many Kagome metals, starting from a single building block, FeGe.

报告人简介：

　　徐远锋，浙江大学研究员。2019年博士毕业于中科院物理所，2019-2022年先后在德国马普所微结构物理所、美国普林斯顿大学物理系从事博士后研究。主要从事凝聚态理论与材料计算研究。2022年入选海外优青，加入浙江大学关联物质研究中心。