Absence of local thermal equilibrium in two models of heat conduction

Abstract

A crucial assumption in the conventional description of thermal conduction is the existence of local thermal equilibrium. We test this assumption in two simple models of heat conduction: a linear chain of planar spins with nearest neighbor couplings and a Lorentz gas. We look at the steady state of the system when the two ends are connected to heat baths at temperatures T₁ and T₂. If T₁ = T₂, the system reaches thermal equilibrium. If T₁≠T₂, there is a heat current through the system, but there is no local thermal equilibrium, even in the limit of large system size, when the heat current goes to zero. We argue that this is due to the existence of an infinity of local conservation laws in their dynamics.