Proposal for the Detection of Magnetic Monopoles in Spin Ice via Nanoscale Magnetometry

TL;DR

This paper proposes using advanced nanoscale magnetometry techniques to detect individual magnetic monopoles in spin ice materials at very low temperatures, enabling direct observation and analysis of monopole dynamics.

Contribution

It introduces a detailed experimental proposal employing three different nanoscale magnetometry platforms to detect magnetic monopoles in spin ice, supported by Monte Carlo simulations.

Findings

Monopoles can be observed at temperatures below 1.5 K.

Noise spectroscopy can reveal monopole fluctuations and interactions.

Three magnetometry methods are analyzed for effectiveness in detection.

Abstract

We present a proposal for applying nanoscale magnetometry to the search for magnetic monopoles in the spin ice materials holmium and dysprosium titanate. Employing Monte Carlo simulations of the dipolar spin ice model, we find that when cooled to below $1.5\,$K these materials exhibit a sufficiently low monopole density to enable the direct observation of magnetic fields from individual monopoles. At these temperatures we demonstrate that noise spectroscopy can capture the intrinsic fluctuations associated with monopole dynamics, allowing one to isolate the qualitative effects associated with both the Coulomb interaction between monopoles and the topological constraints implied by Dirac strings. We describe in detail three different nanoscale magnetometry platforms (muon spin rotation, nitrogen vacancy defects, and nanoSQUID arrays) that can be used to detect monopoles in these experiments, and analyze the advantages of each.