JNCASR-led team discovers wave-like phonon heat transport in Tl2AgI3 enabling ultra-efficient thermal insulators

Key facts

• Researchers at Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru, an autonomous institute of Department of Science and Technology (DST), demonstrated a particle-to-wave-like crossover in phonon transport in the zero-dimensional inorganic metal halide Tl2AgI3.
• The material exhibits an exceptionally low lattice thermal conductivity of about 0.18 W/m·K and becomes nearly temperature independent above around 125 K, signalling a breakdown of the conventional phonon gas model.
• The study, led by Prof. Kanishka Biswas from the New Chemistry Unit (NCU), JNCASR, was published in the Proceedings of the National Academy of Sciences, USA (PNAS).
• State-of-the-art synchrotron X-ray pair distribution function measurements, low-temperature thermal transport experiments, Raman spectroscopy, and first-principles theoretical calculations were combined to reveal coherence-driven wave-like transport overtaking particle-based transport around 175 K.
• The experimental work was led by first author Dr. Riddhimoy Pathak, Ph.D student of Prof. Biswas, with joint first author Mr. Sayan Paul from the Theoretical Sciences Unit (TSU), JNCASR, providing theoretical insight.
• The research benefitted from national supercomputing resources and international synchrotron facilities under the India@DESY programme.