In a macroscopic system, the phenomenological Fourier law is generally satisfied, where the heat conductivity κ is independent on the system size. However, in the one-dimensional (1D) momentum-conserving Fermi-Pasta-Ulam (FPU) lattice, κ diverges with the system size L as κ~L^α, which is called the anomalous heat conduction. A general consensus has been reached that conserved quantities play key roles in the anomalous heat conduction. Correspondingly, a super heat diffusion, whose second moment diverges with time t as t^β with β>1, would occur when the anomalous heat conduction exists. It is expected that the energy diffusion propagator in a 1D nonlinear lattice with three conserved quantities, energy, momentum and stretch, consists of a central heat mode and two sound modes moving with the sound speed, where the heat mode follows a Levy distribution. Here, we study the above mentioned heat transport phenomenon in a 1D lattice with transverse motions and external magnetic field B. The system will stay at a metastable state when B is large. And the property of heat transport in such a metastable state is essentially different from that in the final equilibrium state. In the metastable state our numerical results show normal heat diffusion and normal heat conduction; whereas in the equilibrium case they indicate super heat diffusion and anomalous heat conduction.

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金瑜亮 研究员