Non-Hermitian physics and topological phenomena in convective thermal metamaterials
Non-Hermitian physics and topological phenomena are two hot topics attracted much attention in condensed matter physics and artificial metamaterials. Thermal metamaterials are one type of metamaterials that can manipulate heat on one's own. Recently, it has been found that non-Hermitian physics and topological phenomena can be implemented in purely diffusive systems. However, conduction alone is not omnipotent due to the missing of degrees of freedom. Heat convection, accompanying with conduction, is capable of realizing a large number of phases. In this review, we will present some important works on non-Hermitian and topological convective thermal metamaterials. In non-Hermitian physics, we will first discuss the implementation of exceptional point (EP) in thermal diffusion, followed by high-order EP and dynamic encirclement of EP. We then discuss two works on the extensions of EP in diffusion systems, namely, the chiral thermal behavior in the vicinity of EP and the Weyl exceptional ring. For topological phases, we will discuss two examples: a one-dimensional topological insulator and a two-dimensional quadrupole topological insulator. Finally, we will make a conclusion and present a promising outlook in this area. Convective thermal metamaterials offer an excellent platform for investigating non-Hermitian physics and topological phases. In addition, non-Hermitian and topological thermal metamaterials have great potential for industrial applications.