Scheme: Wolfson Research Merit Awards
Organisation: University College London
Dates: Sep 2014-Aug 2019
Summary: Coulomb's law states that the attraction of positive electric charge to negative electric charge diminishes as the square of the distance between the charges. It determines the properties of materials because they are made of atoms, which consist of positive nuclei and negative electrons. However, electrons in materials can be ripped out of atoms by applying an electric field that is strong enough to overcome the Coulomb attraction. The way that the resulting electric current changes with the strength of the electric field is a mathematical signature of Coulomb's inverse-square law.
Now I have teamed up with collaborators in the UK, France and Japan, to experimentally establish the magnetic equivalent of Coulomb's law of attraction between atom-size packets of magnetic charge, called magnetic monopoles. These monopoles exist in special “spin ice” materials where they form currents analogous to electrical ones, so-called “magnetricity”. By measuring the magnetic field-dependence of these currents, we observed the mathematical form characteristic of the Coulomb attraction of positive and negative magnetic monopoles. This is the first time the Coulomb law has been directly observed in experiment for atom-sized magnetic charges.
The discovery puts magnetic monopoles in spin ice on a very firm basis and may have implications for magnetic technology at very low temperature.