Observation of Magnetic Monopoles in Spin Ice

TL;DR

This study provides experimental evidence for magnetic monopoles in spin ice Dy2Ti2O7, demonstrating their fluctuating behavior and controllable density via temperature and magnetic field, supporting theoretical predictions of magnetic Coulomb interactions.

Contribution

First experimental observation of magnetic monopole excitations in spin ice under magnetic fields, confirming their fluctuating states and Coulomb interactions.

Findings

Monopoles fluctuate between high- and low-density states near the critical point.

Monopole-pair creation follows an Arrhenius law.

Monopole density is controllable by temperature and magnetic field.

Abstract

Excitations from a strongly frustrated system, the kagome ice state of the spin ice Dy2Ti2O7 under magnetic fields along a [111] direction, have been studied. They are theoretically proposed to be regarded as magnetic monopoles. Neutron scattering measurements of spin correlations show that close to the critical point the monopoles are fluctuating between high- and low-density states, supporting that the magnetic Coulomb force acts between them. Specific heat measurements show that monopole-pair creation obeys an Arrhenius law, indicating that the density of monopoles can be controlled by temperature and magnetic field.