ESPCI web site
March 6 at 2:00 pm (Paris time)
Ziman hydrodynamic regime in sapphire
When an ideal insulator is cooled, four regimes of thermal conductivity are expected to emerge one after another. Two of these, the Ziman and the Poiseuille, are hydrodynamic regimes in which collision among phonons are mostly Normal. It has been difficult to observe them, save for a few insulators with high levels of isotopic and chemical purity. In my talk, I will present the results of thermal transport measurements, covering four decades of temperatures between 0.1 K and 900 K, and show that sapphire displays all four regimes, despite its isotopic impurity. In the Ziman regime, the thermal conductivity exponentially increases reaching an amplitude as large as 35,000 W/Km, which is comparable with the maximum thermal conductivity attained by isotopically pure diamond and silicon. I will discuss the robust Ziman regime in sapphire is attributed to by the proximity of optical and acoustic phonon modes, as a consequence of the large number of atoms in the primitive cell.
