Mean free path

About: Mean free path is a research topic. Over the lifetime, 4412 publications have been published within this topic receiving 114418 citations.

Thermal conductivity of Bi2Te3 nanowires: how size affects phonon scattering

Abstract: This work provides an in-depth study of how the thermal conductivity of stoichiometric [110] Bi2Te3 nanowires becomes affected when reducing its diameter from an experimental and theoretical point of view. The thermal conductivity was observed to decrease more than 70% (from 1.78 ± 0.46 W K-1 m-1 to 0.52 ± 0.35 W K-1 m-1) when the diameter of the nanowire was reduced one order of magnitude (from 300 nm to 25 nm). The Kinetic-Collective model was used to understand such a reduction, which can be explained by the impact that surface scattering has in acoustic phonons. The smaller the diameter of the nanowires is, the larger the alteration in the mean free path of the low-frequency phonons is. The model agrees well with the experimental data, and the reduction in the thermal conductivity of the nanowires can be explained in terms of an increment of phonon scattering.

Backscattering in helical edge states from a magnetic impurity and Rashba disorder

Abstract: Transport by helical edge states of a quantum spin Hall insulator is experimentally characterized by a weakly temperature-dependent mean free path of a few microns and by reproducible conductance oscillations, challenging proposed theoretical explanations. We consider a model where edge electrons experience spatially random Rashba spin-orbit coupling and couple to a magnetic impurity with spin $S\ensuremath{\ge}1/2$. In a finite bias steady state, we find for $Sg1/2$ an impurity induced resistance with a temperature dependence in agreement with experiments. Since backscattering is elastic, interference between different scatterers possibly explains conductance fluctuations.

Mean path length invariance in multiple light scattering

Abstract: Our everyday experience teaches us that the structure of a medium strongly influences how light propagates through it. A disordered medium, e.g., appears transparent or opaque, depending on whether its structure features a mean free path that is larger or smaller than the medium thickness. While the microstructure of the medium uniquely determines the shape of all penetrating light paths, recent theoretical insights indicate that the mean length of these paths is entirely independent of any structural medium property and thus also invariant with respect to a change in the mean free path. Here, we report an experiment that demonstrates this surprising property explicitly. Using colloidal solutions with varying concentration and particle size, we establish an invariance of the mean path length spanning nearly two orders of magnitude in scattering strength, from almost transparent to very opaque media. This very general, fundamental and counterintuitive result can be extended to a wide range of systems, however ordered, correlated or disordered, and has important consequences for many fields, including light trapping and harvesting for solar cells and more generally in photonic structure design.

Inhibition of Electron Thermal Conduction by Electromagnetic Instabilities

Abstract: Heat flux inhibition by electromagnetic instabilities in a hot magnetized plasma is investigated Low-frequency electromagnetic waves become unstable due to anisotropy of the electron distribution function The chaotic magnetic field thus generated scatters the electrons with a specific effective mean free path Saturation of the instability due to wave-wave interaction, nonlinear scattering, wave propagation, and collisional damping is considered The effective mean free path is found self-consistently, using a simple model to estimate saturation level and scattering, and is shown to decrease with the temperature gradient length The results, limited to the assumptions of the model, are applied to astrophysical systems For some interstellar clouds the instability is found to be important Collisional damping stabilizes the plasma, and the heat conduction can be dominated by superthermal electrons