Diffusive non-reciprocity and thermal diode

Abstract

Wave propagation and diffusion in linear materials preserve local reciprocity in terms of a symmetric Green's function. For wave propagations, the relation between the fields entering and leaving a system is more relevant than the detailed information about the fields inside it. In such cases, the global reciprocity of the scattering off a system through several ports is more important, which is defined as the symmetric transmission between the scattering channels. When a two-port system supports non-reciprocal (electromagnetic, acoustic) wave propagation, it is a (optical, phonon) diode directly following the definition. However, to date no concrete definition or discussion has been made on the global reciprocity of diffusive processes through a multiple-port system. It thus remains unclear what are the differences and relations between the three concepts, namely local non-reciprocity, global non-reciprocity, and diode effect in diffusion. Here, we provide theoretical analysis on the frequency-domain Green's function and define the global reciprocity of heat diffusion through a two-port system, which has a different setup from that of a thermal diode. We further prove the equivalence between a heat transfer system with broken steady-state global reciprocity and a thermal diode, assuming no temperature-dependent heat generation. The validities of some typical mechanisms in breaking the diffusive reciprocity and making a thermal diode have been discussed. Our results set a general background for future studies on symmetric and asymmetric diffusive processes.

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• Reciprocity of thermal diffusion in time-modulated systems
• Localized heat diffusion in topological thermal materials
• Designing nonlinear thermal devices and metamaterials under the Fourier's law: A route to nonlinear thermotics
• Observation of Multiple Topological Corner States in Thermal Diffusion
• Scattering symmetry of diffusive systems
• Non-Hermitian physics and topological phenomena in convective thermal metamaterials