Abstract
Anomalous energy transport is a widely investigated character in one-dimensional lattice and both phonons and solitons are candidate energy carriers responsible for the thermal conductivity divergence before their mean-free paths. However, it was long believed the contribution of solitons could be neglected even close to the melting point in a real crystalline solid. In this paper, we show that a crossover of wave-packet dynamics, from a phonon- to a soliton-dominated state, occurs in a quasi-one-dimensional molybdenum disulfide $({\mathrm{MoS}}_{2})$ sheet at high temperatures far below its melting point by nonequilibrium and equilibrium molecular dynamics simulations. Divergent sound speed variation and the corresponding heat capacity peaks are observed in the transition-temperature region that is related to a second-order phase transition. We also find that its anomalous energy transport falls into a universality class with thermal conductivity divergence exponent $\ensuremath{\alpha}=2/5$ at a finite length scale within 2000 nm when solitons are excited above 600 K, and the scaling relations derived from the L\'evy walk of energy carriers is fulfilled as $\ensuremath{\alpha}=2\ensuremath{-}1/\ensuremath{\gamma}=\ensuremath{\beta}\ensuremath{-}1$ in the soliton-dominated state above 1800 K. Our results reveal the peculiar solitonlike contribution to thermal conduction at high temperatures in the low-dimensional crystalline solids.
Published Version
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