Observation of ballistic thermal transport in a nonintegrable classical many-body system

We present a compelling observation of ballistic thermal transport in a nonintegrable classical many-body system, substantiated by extending a system with alternating long-range (LR) inverse couplings proposed in a recent study [Yoshimura et al., Phys. Rev. E 105, 024140 (2022)10.1103/PhysRevE.105.024140] from its close-to-linear regime to the fully nonlinear regime. Through this extension, we identify all characteristic hallmarks of ballistic thermal transport, including the ballistic scaling of equilibrium dynamical correlations, size-independent energy current, and flat bulk temperature profile. These features persist for large system sizes (long times), indicating the validity of such ballistic transport in the thermodynamic limit. The underlying mechanism is related to the presence of specific moving energy excitations that seem to be induced by a complex combination of alternating LR inverse couplings and nonlinearity, which enables the regularity in transport within this fully chaotic nonintegrable system. We also discuss the potential connection of these moving energy excitations to traveling discrete breathers.