The free and freer XY models

TL;DR

This paper investigates two variants of the XY model with dynamic interaction networks, revealing phase transitions and clustering behaviors that align with mean-field theory predictions.

Contribution

It introduces the free and freer XY models where the interaction topology can change, extending the understanding of phase transitions in such adaptable networks.

Findings

Both models exhibit phase transitions in dense networks.

Low-temperature phases show clustering and connectivity patterns.

Exponents are consistent with mean-field XY model predictions.

Abstract

We study two versions of the XY model where the spins but also the interaction topology is allowed to change. In the free XY model, the number of links is fixed, but their positions in the network are not. We also study a more relaxed version where even the number of links is allowed to vary, we call it the freer XY model. When the interaction networks are dense enough, both models have phase transitions visible both in spin configurations and the network structure. The low-temperature phase in the free XY model, is characterized by tightly connected clusters of spins pointing in the same direction, and isolated spins disconnected from the rest. For the freer XY model the low-temperature phase is almost completely connected. In both models, exponents describing the magnetic ordering are mostly consistent with values of the mean-field theory of the standard XY model.