Abstract

Bringing two or several systems in contact is an ubiquitous situation in Thermodynamics. In particular, when systems exchange conserve quantities such as energy, volumes or particles, the equilibrium stationary state is described by an equalisation of temperatures, pressures or chemical potentials; the difference of these quantities being interpreted as thermodynamic forces. But when going out-of-equilibrium, the existence of such intensive parameters associated with conserved quantities (like mass or volume) remains an open issue.

During this talk, I will present on simple but generic stochastic out-of-equilibrium systems in weak contact the existence of a thermodynamic potential (at the thermodynamic limit, using large deviation analysis) associated with the number of particles in each sub-systems in contact, from which, under certain assumptions, a notion of chemical potential can be derived. These chemical potentials nevertheless reveal a strong dependence on the contact dynamics, and therefore do not generally obey any equation of state, unlike equilibrium (but like pressure in active particles systems). Several examples ranging from lattice gases to independent self-propelled particles will illustrate the influence of the contact features.