Geometrical aspects of Gigantic Magneto-Electric effect and Quantum Pump

We study the Magneto-Electric (ME) effect from the viewpoint of the Berry phase connection and quantum adiabatic charge transport (QAPT). The linear response theory for the electronic polarization $\vec{P}_{\rm{el}}$ can be interpreted in terms of the flux or the fictitious magnetic field related to the Berry phase in the generalized space which is composed of a crystal momentum and some external parameters. An applied magnetic field modifies the spin configuration, which induces adiabatic deformation of the Bloch wavefunction and results in the electronic polarization given by the total flux penetrating the plaquette spanned by this external parameter and crystal mometum. This provides a new mechanism for the gigantic ME effect. For a cyclic change of the applied magnetic field, even a quantized charge transport is possible.