Seminário Geral: Signatures of phonon hydrodynamics in thermal conductivity

The hydrodynamic regime of phonon flow in a crystal is a wave-like transport regime where phonons do not degrade their momentum. This regime was identified decades ago [1] and is gaining renewed attention in the context of graphene-like two-dimensional systems [2] motivated by the increasing demand for efficient heat removal from nanoelectronic devices [3].

The hydrodynamic flow is revealed in solids by the presence of the second sound and the Poiseuille flow of phonons. The latter can be observed studying thermal conductivity, where a faster-than cubic temperature dependence in a temperature window below the peak is the hallmark of this regime.

In this seminar, I will revise the scattering events that determine the finite thermal conductivity in insulating crystals (Normal, Umklapp, impurities), discussing under which conditions the Poiseuille flow displays in thermal transport. Finally, I will discuss our recently published results on the study of thermal conductivity of SrTiO3 [4], where the emergence of this phenomenon is ascribed to an enhanced space of three-phonon events that conserve momentum, allowing to attain the stricted precondition for the emergence of the hydrodynamic flow without recurring to a high purity sample.

[1]  Beck H. et al. “Phonon hydrodynamics in solids.” Phys status solidi (a) (1974)

[2] Lee S. et al. “Hydrodynamic phonon transport in suspended graphene” Nature Comm (2015)

[3] Cahill D., et al. “Nanoscale thermal transport. II. 2003–2012.” Appl Phys Rev 1.1 (2014)

[4] Martelli V., et al. “Thermal transport and phonon hydrodynamics in strontium titanate.” Phys Rev Lett (2018)