Editor's Summary

3 January 2008

Poles apart

We are familiar with elementary particles that carry either negative or positive electric charge, such as electrons and protons, but there is no evidence of elementary particles with a net magnetic charge. Magnets tend to come with inseparable north and south poles, and there are no known magnetic monopoles despite concerted efforts to find them. But an intriguing theoretical study now proposes that magnetic monopoles may exist, not as elementary particles, but as emergent particles in exotic condensed matter magnetic systems such as 'spin ice'. The theory, based on an analogy to fractional electric charges seen, for example, in quantum Hall systems in two dimensions, can explain a mysterious phase transition that has been observed experimentally in spin ice. The cover, by Alessandro Canossa, depicts a magnetic monopole (red sphere) emerging from break-up of the dipole moment (arrows) of the underlying electronic degrees of freedom in spin ice.

News and Views: Magnetism: Freedom for the poles

Magnetic poles always come in twos, a north and a south. That received wisdom has not stopped physicists from searching for 'monopoles' in accelerators and cosmic rays. Theory now indicates a better place to look.

Oleg Tchernyshyov

doi:10.1038/451022b

Full Text | PDF (156K)

Letter: Magnetic monopoles in spin ice

C. Castelnovo, R. Moessner & S. L. Sondhi

doi:10.1038/nature06433

First paragraph | Full Text | PDF (467K) | Supplementary information