Graded anharmonic crystals as genuine thermal diodes: Analytical description of rectification and negative differential thermal resistance

We address the heat flow study starting from microscopic models of matter: we develop an approach and investigate some anharmonic graded mass crystals, with weak interparticle interactions. We calculate the thermal conductivity, and show the existence of rectification and negative differential thermal resistance. Our formalism allows us to understand the mechanism behind the phenomena, and shows that the properties of graded materials make them genuine thermal diodes.