Thermal conductance of the Fermi-Pasta-Ulam chains: Atomic to mesoscopic transition

We demonstrate that in the atomic-scale limit the thermal conductance $\mathcal{K}$ of the FPU model and its variants strongly deviates from the mesoscopic behavior due to the relevance of contact resistance. As a result, atomic chains follow $\log \mathcal{K}=\nu \log T$, where the power law coefficient $\nu$ is exactly two times larger than the mesoscopic value. We smoothly interconnect the atomic and mesoscopic limits, and demonstrate that this turnover behavior takes place in other nonlinear FPU-like models. Our results are significant for nanoscale applications, manifesting an atomic thermal conductance with temperature scaling superior to the mesoscopic limit.