Researchers demonstrated a thermal conductivity of 0.08 W/m-K at room temperature in single-crystalline CsAg2I3 by exploiting vortical phonon vibrations, according to a study published in Nature Communications.
The study examined how vortical modes of polarized phonons alter heat transport in solid lattices. In CsAg2I3, anisotropically bonded iodine atoms form low-lying transverse optical phonons that expand the phonon scattering phase space. These vortical modes arise primarily from chiral symmetric operations acting on the material's iodine sites.
The resulting vortical motion induces two-dimensional short-range ordering of atomic clusters. This structural ordering creates phonon scattering centers with diameters on the order of approximately two primitive cells, suppressing heat propagation through the crystal lattice.
Co-lead authors Qingyu Bai and Long Yang conducted the research alongside teams from Tongji University, Shanghai Jiao Tong University, and the University of Hong Kong, among other institutions. The researchers gathered experimental data using synchrotron X-ray diffuse scattering, ab initio molecular dynamics simulations, and inelastic neutron scattering at the China Spallation Neutron Source, the J-PARC Materials and Life Science Experimental Facility, the Center for High-Energy X-ray Sciences, and the MERLIN spectrometer at the ISIS Neutron and Muon Source.
