  We theoretically investigate heat transport in hybrid normal
metal-superconductor (NS) nanojunctions focusing on the effect of thermal
rectification. We show that the heat diode effect in the junction strongly
depends on the transmissivity and the nature of the NS contact. Thermal
rectification efficiency can reach up to 123% for a fully-transmissive
ballistic junction and up to 84% in diffusive NS contacts. Both values exceed
the rectification efficiency of a NIS tunnel junction (I stands for an
insulator) by a factor close to 5 and 3, respectively. Furthermore, we show
that for NS point-contacts with low transmissivity, inversion of the heat diode
effect can take place. Our results could prove useful for tailoring heat
management at the nanoscale, and for mastering thermal flux propagation in
low-temperature caloritronic nanocircuitry.
