Anatomy of a Spin: The Information-Theoretic Structure of Classical Spin Systems

TL;DR

This paper applies an information-theoretic approach to analyze the collective organization in classical spin systems, revealing how entropy decompositions relate to emergent structures and phase transitions.

Contribution

It introduces a novel entropy decomposition method for classical spin systems and demonstrates its effectiveness on various lattice models, providing new insights into their organization.

Findings

Entropy decomposition reveals emergent structures near phase transitions.

Different spin motifs influence dependencies and organization.

Method generalizes across lattice types and models.

Abstract

Collective organization in matter plays a significant role in its expressed physical properties. Typically, it is detected via an order parameter, appropriately defined for each given system's observed emergent patterns. Recent developments in information theory, however, suggest quantifying collective organization in a system- and phenomenon-agnostic way: decompose the system's thermodynamic entropy density into a localized entropy, that solely contained in the dynamics at a single location, and a bound entropy, that stored in space as domains, clusters, excitations, or other emergent structures. We compute this decomposition and related quantities explicitly for the nearest-neighbor Ising model on the 1D chain, the Bethe lattice with coordination number k=3, and the 2D square lattice, illustrating its generality and the functional insights it gives near and away from phase transitions. In particular, we consider the roles that different spin motifs play (in cluster bulk, cluster edges, and the like) and how these affect the dependencies between spins.