Spontaneous currents and charge redistribution in Mott insulators

The standard view is that at low energies Mott insulators exhibit only magnetic properties while charge degrees of freedom are frozen out as the electrons become localized by a strong Coulomb repulsion. We demonstrate that this is in general not true: for certain spin textures \textit{spontaneous circular electric currents} or \textit{nonuniform charge distribution} exist in the ground state of Mott insulators. The latter can give a purely electronic mechanism of \textit{multiferroic behaviour}. In addition, low-energy ``magnetic'' states contribute comparably to the dielectric and magnetic functions, leading to interesting phenomena such as the electric field-induced ``ESR'' transitions, rotation the electric field polarization and resonances which may be common for both functions producing a negative refraction index in a window of frequencies.