Abstract
Nanotubes have recently been experimentally demonstrated to be perfect phonon waveguides. To explore the underlying physics, we present atomic scale calculations of thermal transport in carbon nanotubes under radial strain using the nonequilibrium Green's function method. It is found that the thermal conductance exhibits a robust linear response behavior to radial strain over the whole elastic range. A detailed analysis of phonon transmission reveals that an elastic radial strain can be viewed as a perturbation of the transport of most of the low-frequency phonons. This is attributed to the unique bonding configuration of nanotubes, which can be well preserved even under severe deformation. Such a structural response to deformation, which is rare in other systems, explains the robust thermal transport in nanotubes against severe radial deformation.
Highlights
Nanotubes have recently been experimentally demonstrated to be perfect phonon waveguides
We explore the general features of the radial-strain-dependent thermal conductance at different temperatures, and discuss the related physical mechanism
Radial strain in CNTs can be viewed as a perturbation of the transport of low-frequency phonons; a robust linear response of thermal conductance to radial strain appears in the entire elastic range at low temperatures
Summary
The transport system can be divided into three parts: two semi-infinite pristine CNTs serving as reservoirs and a deformed central part (transport channel), as shown in figure 1. To apply a specified radial strain, two rows of carbon atoms on opposite sides of CNTs are fixed during the structural relaxation. In all the structural relaxations, the length of the central region is selected long enough to include a complete deformation area from the confined regime to the pristine CNT reservoirs. The NEGF method can exactly deal with the thermal transport of the system in which phonon–phonon scattering and electron–phonon scattering are neglected, which is reasonable at a moderate temperature for a sample a few microns long, verified by experiments [3, 4, 11, 12]. Only the heat current mediated by phonons is considered, while the contribution from electrons is neglected [8, 9]
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