Experimental Proof of a Magnetic Coulomb Phase

TL;DR

This paper provides experimental evidence for a magnetic Coulomb phase in the spin ice material Ho2Ti2O7, demonstrating the presence of deconfined magnetic monopoles and Dirac strings through polarized neutron scattering.

Contribution

First experimental proof of a magnetic Coulomb phase in a real material, confirming theoretical predictions about magnetic monopoles in spin ice.

Findings

Demonstrates the existence of an almost perfect Coulomb phase in Ho2Ti2O7.

Shows temperature-dependent scattering consistent with deconfined magnetic monopoles.

Separates magnetic correlation contributions using polarized neutron scattering.

Abstract

Spin ice materials are magnetic substances in which the spin directions map onto hydrogen positions in water ice. Recently this analogy has been elevated to an electromagnetic equivalence, indicating that the spin ice state is a Coulomb phase, with magnetic monopole excitations analogous to ice's mobile ionic defects. No Coulomb phase has yet been proved in a real magnetic material, as the key experimental signature is difficult to resolve in most systems. Here we measure the scattering of polarised neutrons from the prototypical spin ice Ho2Ti2O7. This enables us to separate different contributions to the magnetic correlations to clearly demonstrate the existence of an almost perfect Coulomb phase in this material. The temperature dependence of the scattering is consistent with the existence of deconfined magnetic monopoles connected by Dirac strings of divergent length.