| Phononics,a new subject developed in recent years,aims to explore and analyze how to control heat flux by adjusting specific frequencies.On the basis of this,we design the thermology device which can control the heat and process the thermal signal,so that the heat flux can be transmitted according to the design intention of the people.But since phonon is not a real physical particle,it is a virtual cluster of energy without mass and charge to understand the vibration of the lattice,therefore it is not directly affected by gravity and electromagnetic force,which brings great challenge to the accurate control of heat flux.In this paper,heat controlling of low dimensional nonlinear lattice system is studied by the method of non-equilibrium molecular dynamics.The dependence of model parameters and external conditions on thermal rectification and negative differential thermal resistance is analyzed.The aim is to design more efficient theoretical models and to find more appropriate parameters.In addition,due to the phonon devices are designed in micro and nanometer size,the influence of quantum effect on the thermal transport property of lattice system should be taken into account in the same time.These results provide some guides for improving the efficiency of thermal devices and designing new thermal devices.The research contents in this paper mainly focus on the following aspects:1.We study the negative differential thermal resistance of the coupled system composed of Frenkel-Kontorova(FK)lattices and Fermi-Pasta-Ulama-Ulam(FPU)lattices coupled by harmonic interaction.By adjusting the temperature of heat bath,we make the system in the case of different temperature difference,after the system reaches the non-equilibrium steady state,we simulated the heat flux flow through the system with the help of non-equilibrium molecular dynamics method.The results show that negative differential thermal resistance exists in the heterogeneity coupling chain,and the temperature region in which this phenomenon occurs is closely related to the system size,interface coupling strength and average temperature.In addition,we can control the region of negative differential thermal resistance by adjusting the size of FK segment,but the change of FPU segment size has no great influence on the region where negative differential thermal resistance appears.2.We have studied the regulation of heat flux by external on-site potential,the purpose is to analyse the effect of the double well on-site potential on the thermal rectifying properties of the mass gradient lattice chain,the double well onsite potential is divided into the harmonic part and the anharmonic part.The equation of motion of particles is obtained by Hamiltonian canonical equation,and then the Runge-Kutta method is used to solve the differential equation numerically.After a long relaxation,we observed that onsite potential changed not only the magnitude of the rectifier but also its direction3.Under the micro or mesoscopic size,the quantum effect cannot be ignored,which will have a great influence on the efficiency of the micro and nano thermal devices,and even destroy its regulation function.We use a wave packet variational method to study the thermal transport properties of one-dimensional Frenkel-Kontorova nonlinear lattice after considering the quantum effect.In this method,each crystal lattice is described by a Jackiw-Kerman wave function,and then the direct product of the single particle wave function is set as the multibody wave function of the system.Then with the help of the Dirac time-dependent variational principle,the equation of motion of variational parameters is obtained,that is,the dynamic evolution equation of the system.After a long relaxation,the numerical simulation results show that the quantum effect causes the change of heat conduction behavior in the nonlinear lattice system,and the stronger the quantum effect,the greater the heat flow through the system. |
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