Extending spin ice concepts to another geometry: the artificial triangular spin ice

TL;DR

This paper introduces a new artificial triangular spin ice system, exploring its ground state, excitations, and thermodynamic behavior, revealing universal monopole charges and tunable string tensions, with a phase transition in the Ising class.

Contribution

It extends spin ice concepts to a triangular geometry, demonstrating monopole-like excitations and phase transition properties not previously studied in this configuration.

Findings

Monopole excitations behave as Nambu monopoles with universal charge.

String tension can be tuned by system geometry.

System exhibits a phase transition in the Ising universality class.

Abstract

In this work we propose and study a realization of an artificial spin ice-like system, not based on any real material, in a triangular geometry. At each vertex of the lattice, the "ice-like rule" dictates that three spins must point inward while the other three must point outward. We have studied the system's ground-state and the lowest energy excitations as well as the thermodynamic properties of the system. Our results show that, despite fundamental differences in the vertices topologies as compared to the artificial square spin ice, in the triangular array the lowest energy excitations also behave as a kind of Nambu monopoles (two opposite monopoles connected by an energetic string). Indeed, our results suggest that the monopoles charge value may have a universal value while the string tension could be tuned by changing the system's geometry, probably allowing the design of systems with different string tensions. Our Monte Carlo results suggest a phase transition in the Ising universality class where the mean distance between monopoles and anti-monopoles increases considerably at the critical temperature. The differences on the vertices topologies seem to facilitate the experimental achievement of the system's ground-state, thereby allowing a more detailed experimental study of the system's properties.