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Electric dipoles on magnetic monopoles in spin ice

The close connection of electricity and magnetism is one of the cornerstones of modern physics. This connection plays crucial role from the fundamental point of view and in practical applications, including spintronics and multiferroic materials. A breakthrough was a recent proposal that in magnetic materials called spin ice the elementary excitations have a magnetic charge and behave as magnetic monopoles. I show that, besides magnetic charge, there should be an electric dipole attached to each magnetic monopole. This opens new possibilities to study and to control such monopoles by electric field. Thus the electric--magnetic analogy goes even further than usually assumed: whereas electrons have electric charge and magnetic dipole (spin), magnetic monopoles in spin ice, while having magnetic charge, also have electric dipole.