title: Magnetic monopoles in spin ice.
abstract: Electrically charged particles, such as the electron, are ubiquitous. In contrast, no elementary particles with a net magnetic charge have ever been observed, despite intensive and prolonged searches (see ref. 1 for example). We pursue an alternative strategy, namely that of realizing them not as elementary but rather as emergent particles-that is, as manifestations of the correlations present in a strongly interacting many-body system. The most prominent examples of emergent quasiparticles are the ones with fractional electric charge e/3 in quantum Hall physics. Here we propose that magnetic monopoles emerge in a class of exotic magnets known collectively as spin ice: the dipole moment of the underlying electronic degrees of freedom fractionalises into monopoles. This would account for a mysterious phase transition observed experimentally in spin ice in a magnetic field, which is a liquid-gas transition of the magnetic monopoles. These monopoles can also be detected by other means, for example, in an experiment modelled after the Stanford magnetic monopole search.
authors.affiliation: Rudolf Peierls Centre for Theoretical Physics, Oxford University, Oxford OX1 3NP, UK. castel@physics.ox.ac.uk
authors.forename: C
authors.initials: C
authors.lastname: Castelnovo
authors.forename: R
authors.initials: R
authors.lastname: Moessner
authors.forename: S L
authors.initials: SL
authors.lastname: Sondhi