  Rectification of heat transfer in nanodevices can be realized by combining
the system inherent anharmonicity with structural asymmetry. we analyze this
phenomenon within the simplest anharmonic system -a spin-boson nanojunction
model. We consider two variants of the model that yield, for the first time,
analytical solutions: a linear separable model in which the heat reservoirs
contribute additively, and a non-separable model suitable for a stronger
system-bath interaction. Both models show asymmetric (rectifying) heat
conduction when the couplings to the heat reservoirs are different.
