Spin chirality and nontrivial charge dynamics in frustrated Mott insulators: spontaneous currents and charge redistribution

The standard point of view is that at low energies Mott insulators exhibit only magnetic properties, while charge degrees of freedom are frozen out because electrons are localized. We demonstrate (Bulaevskii et al 2008 Phys. Rev. B 78 024402) that in general this is not true: for certain spin textures there exist quite nontrivial charge effects in the ground and lowest excited states. We show that in frustrated systems spontaneous orbital currents may exist in the ground state, proportional to the scalar spin chirality. For other spin structures spontaneous charge redistribution may exist, so that the average charge at a site is different from 1. This can lead to the appearance of dipole moments and possibly of the net spontaneous polarization. This is a novel, purely electronic mechanism of multiferroic behaviour. We also discuss some dynamic consequences, such as dipole-active 'ESR' transitions. Also, the possibility of using chirality instead of spin in memory applications is briefly discussed.