(Anti)ferroelectricity Induced Dual-Breathing Mode in Bulk Kagome Semiconductor Nb ₃ I ₈

The kagome lattice has long been a subject of fascination for physicists due to its rich physics, encompassing phenomena such as superconductivity, charge density waves, and flat bands. In this work, we report the discovery of a novel ferroelectricity-induced dual-breathing mode in the kagome semiconductor Nb 3 I 8 . This dual-breathing mode involves both intralayer and interlayer breathing motions that are driven by the polarization within the layers. We demonstrate that, both theoretically and experimentally, such a breathing pattern will disappear in the absence of ferroelectric polarization in each layer. This discovery not only broadens our understanding of complex interactions within kagome lattices but also paves the way for the development of new types of electronic devices based on ferroelectricity.