Thermal Rectification by Ballistic Phonons in Asymmetric Nanostructures

In analogy to an electrical diode, a thermal rectifier transports heat more easily in one direction than in the reverse direction. Among various possible nanoscale rectification mechanisms, a ballistic rectifier relies on asymmetric scattering of energy carriers, as has been suggested for phonon transport in a sawtooth nanowire [S. Saha, L. Shi, & R. Prasher, IMECE 2006] or nanowire with special surface specularity function [N.A. Roberts and D.G. Walker, ITherm 2008]. We have used a Landauer-Buttiker method as well as a Monte Carlo method to model the asymmetric heat transport in such nanostructures, with careful attention to boundary conditions that satisfy the 2nd Law of Thermodynamics. The calculations show that ballistic rectification is only significant at relatively large “thermal bias,” which causes significant anisotropy in the distribution function of energy carriers emitted at each of the two thermal contacts. We also propose experiments to observe this phenomenon using either phonons or photons.