Strain-Modulated Phase Transition in 2D V₃F₈ Kagome Lattice with Topological Flat Band

Abstract

Quantum-scale interplay between geometry, topology, and correlation is at the forefront of fundamental physics. Kagome magnets are expected to support intrinsic Chern quantum phases due to the unusual lattice geometry and broken timereversal symmetry. However, the flat band is rarely detected just at the Fermi level, which would be crucial for the realization of emerging flat-band physics. Furthermore, a majority of Kagome materials discovered exhibit metallic behavior, hindering their suitability for utilization in logic devices. Here, by first-principles calculations, we observe a striking Fermi-level flat band in 2D ferromagnetic V 3 F 8 as a typical signature of the electronic Kagome lattice. By applying a uniaxial strain, the topological edge states can be modulated to cross the Fermi level, accompanied by the transition from half-metal to semiconductor. We further engineer this material with lithium (Li) atom doping to induce more topological flat bands and enhance the Curie temperature. Our work establishes a Fermi-level flat band in a Kagome magnet as an exciting quantum platform.