Non-Fourier heat conduction in a single-walled carbon nanotube: Classical molecular dynamics simulations

Non-stationary heat conduction in a single-walled carbon nanotube was investigated by applying a local heat pulse with duration of sub-picoseconds. The investigation was based on classical molecular dynamics simulations, where the heat pulse was generated as coherent fluctuations by connecting a thermostat to the local cell for a short duration. The heat conduction through the nanotube was observed in terms of spatio-temporal temperature profiles. Results of the simulations exhibit non-Fourier heat conduction where the distinct amount of heat is transported in a wavelike form. The geometry of carbon nanotubes allows us to observe such a phenomenon in the actual scale of the material. The resulting spatio-temporal profile was compared with the available macroscopic equations so called non-Fourier heat conduction equations in order to investigate the applicability of the phenomenological models to the quasi-one-dimensional system. The conventional hyperbolic diffusion equation fails to predict the heat conduction due to the lack of local diffusion. It is shown that this can be remedied by adopting the model with dual relaxation time. Further modal analyses using wavelet transformations reveal a significant contribution of the optical phonon modes to the observed wavelike heat conduction. The result suggests that, in carbon nanotubes with finite length where the long wavelength acoustic phonons behave ballistic, even optical phonons can play a major role in the non-Fourier heat conduction.