Claudio Castelnovo (Ph.D. 2006) has been awarded the 2012 EPS Condensed Matter Division Europhysics Prize for the prediction of magnetic monopoles in spin ice. The prize was shared with experimentalists who observed the effect via neutron scattering measurements on dysprosium titanate.

The effect is an example of fractionalization phenomena, whereby the elementary excitations of the system have charges that are only a fraction of the fundamental constituents. The notion of fractionalization first appeared in physics through the work of Roman Jackiw and Claudio Rebbi, who showed that excitations with half the charge of the electron appear around certain topological defects. In the case of spin ice the fundamental constituents are magnetic dipoles, but the magnetic monopoles predicted by Claudio Castelnovo emerge as the deconfined elementary excitations of the effective gauge theory describing spin ice.