  Systems in which the heat flux depends on the direction of the flow are said
to present thermal rectification. This effect has attracted much theoretical
and experimental interest in recent years. However, in most theoretical models
the effect is found to vanish in the thermodynamic limit, in disagreement with
experiment. The purpose of this paper is to show that the rectification may be
restored by including an energy-conserving noise which randomly flips the
velocity of the particles with a certain rate $\lambda$. It is shown that as
long as $\lambda$ is non-zero, the rectification remains finite in the
thermodynamic limit. This is illustrated in a classical harmonic chain subject
to a quartic pinning potential (the $\Phi^4$ model) and coupled to heat baths
by Langevin equations.

Statistical Mechanics