Magnetic monopoles in spin ice

• Published in: Nature Vol. 451; no. 7174; pp. 42 - 45
• Main Authors: Moessner, R, Castelnovo, C, Sondhi, S. L
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 03.01.2008; Nature Publishing; Nature Publishing Group
• Subjects: Charge; Charged particles; Condensed Matter; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electric charge; Electric properties; Electronics; Exact sciences and technology; High Energy Physics - Theory; Humanities and Social Sciences; Ice; letter; Magnetic fields; Magnetic monopoles; Magnetic properties; Magnetic properties and materials; Magnetism; Mechanical properties; Monopoles; multidisciplinary; Other; Physics; Science; Science (multidisciplinary); Searching; Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.); Spin ice; United States; United Kingdom; Germany; Magnetic monopoles; Phase diagrams; N-body problems; Dipole moments; Spin ice; Excited states; Diamond structure; Pyrochlore type compound; Structural models
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature06433

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.