Collective oscillations in a three-dimensional spin model with non-reciprocal interactions

TL;DR

This paper investigates how collective oscillations emerge in a 3D spin model with non-reciprocal interactions, revealing a two-step phase transition process involving local noisy oscillators and their synchronization.

Contribution

It introduces a detailed analysis of the phase transition mechanism in a non-reciprocal spin model, combining numerical simulations with analytical derivations of coupled Langevin equations.

Findings

Identification of a continuous phase transition to global oscillations.

Discovery of two successive phase transitions: local noisy oscillators and their synchronization.

Derivation of a phase diagram from coupled Langevin equations.

Abstract

We study the onset of collective oscillations at low temperature in a three-dimensional spin model with non-reciprocal short-range interactions. Performing numerical simulations of the model, the presence of a continuous phase transition to global oscillations is confirmed by a finite-size scaling analysis. By systematically varying the interaction range, we show that collective oscillations in this spin model actually result from two successive phase transitions: a mean-field phase transition over finite-size neighborhoods, which leads to the emergence of local noisy oscillators, and a synchronization transition of local noisy oscillators, which generates coherent macroscopic oscillations. Using a Fokker-Planck equation under a local mean-field approximation, we derive from the spin dynamics coupled Langevin equations for the complex amplitudes describing noisy oscillations on a mesoscopic scale. The phase diagram of these coupled equations is qualitatively obtained from a fully-connected (mean-field) approximation. This analytical approach allows us to clearly disentangle the onset of local and global oscillations, and to identify the two main control parameters, expressed as combinations of the microscopic parameters of the spin dynamics, that control the phase diagram of the model.