Unconventional relaxation of hydrodynamic modes in anharmonic chains under strong pressure fluctuations

We develop an effective numerical scheme to capture hydrodynamic (HD) modes in general classical anharmonic chains. This scheme is based on the HD theory suggested by Ernst-Hauge-van Leeuwen, which takes full role of pressure fluctuations into account. With this scheme we show that the traditional pictures given by the current nonlinear fluctuating HD theory are valid only when the system's pressure is zero and the pressure fluctuations are weak. For nonvanishing pressure, the HD modes can, however, respond to small and large pressure fluctuations and relax in some distinct manners. Our results shed new light on understanding thermal transport from the perspective of HD theory.