On the formation/dissolution of equilibrium droplets

We consider liquid-vapor systems in finite-volume V ⊂ R d at parameter values corresponding to phase coexistence and study droplet formation due to a fixed excess δN of par- ticles above the ambient gas density. We identify a dimensionless parameter ∆ ∼ (δN) (d+1)/d /V and a universal value ∆c =∆ c(d), and show that a droplet of the dense phase occurs when- ever ∆ > ∆c, while, for ∆ < ∆c, the excess is entirely absorbed into the gaseous background. When the droplet first forms, it comprises a non-trivial, universal fraction of excess particles. Similar reasoning applies to generic two-phase systems at phase coexistence including solid/gas —where the "droplet" is crystalline— and polymorphic systems. A sketch of a rigorous proof for the 2D Ising lattice gas is presented; generalizations are discussed heuristically.