Collective and hydrodynamic behavior in thermal transport.
Seminar author:Xavier Alvarez Calafell
Event date and time:10/25/2018 12:00:pm
Event location:GIQ Seminar Room (C5/262)
Event contact:Xavier.Alvarez@uab.cat
Recent experiments using ultrafast laser heating on nanoscale samples have shown significant discrepancies respect to Fourier’s law [1-3]. The reason behind this anomalous behavior is related with the conservation of momentum in phonon-phonon collisions. This conservation law imposes some restrictions on the distribution function of the phonons in a way that these particles cannot move independently and have to move in a coherent form. It will be shown that in this regime a generalized entropy can be defined in terms of the mean energy and the heat flux. The formalism used for this has several connections with Information Theory.
When momentum conservation is important, a nonlocal length can be defined to determine the region where the phonons are connected. Kinetic-Collective Model (KCM) has been developed to describe heat transport at these scales through the use of this nonlocal length and the equivalent time scale [4,5]. The consequence is that the discrepancies respect Fourier predictions are due the emergence of hydrodynamic behavior. We use KCM equations to interpret some the experiments and show that their interpretation into the light of KCM could be indicating the presence of hydrodynamic phenomena like viscosity and vorticity [6].
References
[1] J. A. Johnson et al., Physical Review Letters, 110, 025901 (2013).
[2] R. B. Wilson and D. G. Cahill, Nature Communications, 5, 5075 (2014).
[3] K. M. Hoogeboom-Pot et al., PNAS, 112, 201503449 (2015).
[4] P. Torres et al., Physical Review B, 95, 165407 (2017)
[5] C. de Tomas et al., Journal of Applied Physics, 118, 134305 (2015).
[6] A. Ziabari et al., Nature Communications., 9(1), 255 (2018).