Quasi-Ballistic Heat Conduction due to Lévy Phonon Flights in Silicon Nanowires

Abstract

Future of silicon-based microelectronics relies on solving the heat dissipation problem. A solution may lie in a nanoscale phenomenon known as ballistic heat conduction, which implies heat conduction without heating the conductor. But, attempts to demonstrate this phenomenon experimentally are controversial and scarce whereas its mechanism in confined nanostructures is yet to be fully understood. Here, we experimentally demonstrate quasiballistic heat conduction in silicon nanowires (NWs). We show that the ballisticity is strongest in short NWs at low temperatures but weakens as the NW length or temperature is increased. Yet, even at room temperature, quasi-ballistic heat conduction remains visible in short NWs. To better understand this phenomenon, we probe directionality and lengths of phonon flights. Our experiments and simulations show that the quasi-ballistic phonon transport in NWs is the Lévy walk with short flights between the NW boundaries and long ballistic leaps along the NW.

Enhanced thermal conduction by surface phonon-polaritons

“…To further reduce the noise, we accumulate the signal for 1 min, which consists of 10 3 of such iterations. More details of our experimental setup can be found in the literature (34). Last, the measured temporal variations of temperature are combined with an analytical model ("Heat diffusion model" section in the Supplementary Materials) to extract the in-plane thermal conductivity of our SiN membranes.…”

Unsteady ballistic heat transport in harmonic crystals with polyatomic unit cell

“…1 For analytical derivations, position vectors are more convenient than indices, because number of indices depends on space dimensionality. 2 N is equal to number of particles in the unit cell multiplied by number of degrees of freedom per particle. 3 A lattice is referred to as simple lattice, if it coincides with itself under shift by a vector connecting any two particles.…”

Ballistic resonance and thermalization in the Fermi-Pasta-Ulam-Tsingou chain at finite temperature

“…For example, recent theoretical [2-4] and experimental studies [5][6][7][8][9] show that at micro-and nanoscale the Fourier law of heat conduction can be violated. In particular, ballistic regime of heat transport is observed [10,11].A convenient model for investigation of thermomechanical processes at micro-and nanoscale is the Fermi-Pasta-Ulam (FPU) chain [12]. Despite the apparent simplicity of the model, analytical description of thermoelasticity, heat transport and energy conversion in the FPU chain remains a serious challenge for theoreticians.Several anomalies of thermomechanical behavior are observed for the FPU chain.…”

“…For example, recent theoretical [2][3][4] and experimental studies [5][6][7][8][9] show that at micro-and nanoscale the Fourier law of heat conduction can be violated. In particular, ballistic regime of heat transport is observed [10,11].…”