II ICTP-SAIFR Condensed Matter Theory in the Metropolis

Under the conditions of phase separation, systems present an interface between the coexisting phases. In experiments, coexistence is identified through the presence of a plateau in thermodynamic potential isotherms. Given the scarcity of exact solutions for satistical model systems, coexistence is frequently analysed in terms of mean field treatments, or of numerical simulations. Under both treatments, thermodynamic potentials display loops in the phase separating region. The origin of such apparently unstable behaviour, forbidden by the 2nd Law, is attributed to interface tension, in the case of numerical experiments for spin-like models, as indicator of chain colapse for polymer models, or even as a consequence of long-range interactions. In this work, we show that proper interpretation of the measured thermodynamic potentials should eliminate the violation of thermodynamic convexity. New questions may also arise.