Dirac Strings and Magnetic Monopoles in Spin Ice Dy2Ti2O7

TL;DR

This paper demonstrates the existence of Dirac strings and emergent magnetic monopoles in the spin ice Dy2Ti2O7 using neutron scattering and magnetic field manipulation, providing evidence for monopole-like quasiparticles in condensed matter.

Contribution

It provides experimental evidence for Dirac strings and magnetic monopoles in spin ice, advancing understanding of emergent quasiparticles in frustrated magnetic systems.

Findings

Presence of Dirac strings confirmed by neutron scattering.

Magnetic monopoles behave as a Coulomb gas.

Magnetic field controls string density and orientation.

Abstract

While sources of magnetic fields - magnetic monopoles - have so far proven elusive as elementary particles, several scenarios have been proposed recently in condensed matter physics of emergent quasiparticles resembling monopoles. A particularly simple proposition pertains to spin ice on the highly frustrated pyrochlore lattice. The spin ice state is argued to be well-described by networks of aligned dipoles resembling solenoidal tubes - classical, and observable, versions of a Dirac string. Where these tubes end, the resulting defect looks like a magnetic monopole. We demonstrate, by diffuse neutron scattering, the presence of such strings in the spin-ice Dy2Ti2O7. This is achieved by applying a symmetry-breaking magnetic field with which we can manipulate density and orientation of the strings. In turn, heat capacity is described by a gas of magnetic monopoles interacting via a magnetic Coulomb interaction.