Microcanonical phase diagrams of short-range ferromagnets

TL;DR

This paper explores how the phase diagrams of short-range ferromagnets differ when analyzed in the microcanonical ensemble compared to the canonical ensemble, revealing unique features with implications for various physical systems.

Contribution

It demonstrates the distinct structure of microcanonical phase diagrams for short-range ferromagnets and discusses their physical implications, which had not been thoroughly examined before.

Findings

Microcanonical phase diagrams differ significantly from canonical ones.

Distinct features include possible negative specific heat regions.

Implications for nuclear fragmentation, surface adatoms, and cold atom systems.

Abstract

A phase diagram is a graph in parameter space showing the phase boundaries of a many-particle system. Commonly, the control parameters are chosen to be those of the (generalized) canonical ensemble, such as temperature and magnetic field. However, depending on the physical situation of interest, the (generalized) microcanonical ensemble may be more appropriate, with the corresponding control parameters being energy and magnetization. We show that the phase diagram on this parameter space looks remarkably different from the canonical one. The general features of such a microcanonical phase diagram are investigated by studying two models of ferromagnets with short-range interactions. The physical consequences of the findings are discussed, including possible applications to nuclear fragmentation, adatoms on surfaces, and cold atoms in optical lattices.