A microcanonical approach to criticality in the mean-field $\phi^4$ model: evidence of intrinsic microcanonical structure before the thermodynamic limit (opens in new tab)

Collective critical behavior is often identified with thermodynamic nonanalyticities and divergences emerging only in the infinite-size limit. Here we adopt a complementary viewpoint: criticality is a structural property due to the rearrangement of the interactions among system's constituents that already exists at finite size and becomes singular only asymptotically. We show that the microcanonical entropy derivatives provide a natural finite-$...