Researchers demonstrated breathing ferroelectricity, flat electronic bands, and multiple chiral phonons in the van der Waals layered material Nb3Cl8, according to a study published in Nature Communications on August 8, 2026.
The material integrates an intralayer breathing Kagome lattice with alternating van der Waals gaps between adjacent layers. Experiments showed that its breathing ferroelectricity originates from an alternating breathing-in and breathing-out distortion of triangular crystal units through a Kagome state.
Optical characterization showed clear distinctions based on sample thickness. In thin states, Nb3Cl8 exhibited exciton-like absorption peaks involving flat bands, whereas thick states exhibited a semiconductor-like absorption edge. The authors attributed this variation to interlayer interactions and stronger thickness-induced photon absorption, with measured energy levels aligning with theoretical calculations.
Measurements across changing temperatures tracked several temperature-induced transitions related to magnetic properties and electronic phases in both the flat bands and phonon modes. The characterizations also documented strong optical activity alongside multiple chiral phonons across the crystal structure.
Yilun Yu, Fengrui Sui, Beituo Liu, and Shuai Yang contributed equally to the research, which involved teams from East China Normal University, Shanghai University, Zhengzhou Police University, and the Shanghai Institute of Technical Physics. Financial support was provided by the National Natural Science Foundation of China, the Natural Science Foundation of Shanghai, and the Space Application System of China Manned Space Program.
