Colloquium
Department of Physics, NCU
Non-Fourier Thermal Conductors
Speaker
張之威 博士
Dr. Chih-wei Chang
Center for Condensed Matter Sciences, NTU
Date 2013.9.24 (Tue)
Time 14:00
Place S4-625
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Fourier’s law of thermal conduction is perhaps the last empirical law of physics whose foundation is still not clear to physicists. Starting from 1930s, many people have tried to derive Fourier’s law from statistical mechanics but the criteria of the Fourier’s law still remain unknown. Unfortunately, due to the dearth of suitable experimental techniques and materials, the studies on this topic were limited to purely theoretical investigations for past decades. In this colloquium, I will present our recent experimental works starting to shred lights on the phenomena of non-Fourier thermal conduction in SiGe nanowires and in carbon nanotubes. For SiGe nanowires, we discover unprecedented robust ballistic thermal conduction persisting over 8.3 micrometers at room temperature, leading to non-conventional contact thermal resistance and non-additive thermal resistance in series. For ultralong carbon nanotubes, we find that their thermal conductivities increase with their lengths without signs of saturation and reach an unprecedented high value at room temperature for millimeter-long nanotubes. Our results suggest that the overlooked contributions of low frequency phonons are the possible origins for these unusual phenomena.