Relationship between ferroelectricity and Dzyaloshinskii-Moriya interaction in multiferroics and the effect of bond-bending C. D. Hu Department of Physics and Center for Theoretical Sciences National Taiwan University Taipei, Taiwan Republic of China Abstract We studied the microscopic mechanism of multiferroics, in particular with the ”spin current” model (H. Katsura, N. Nagaosa and A. V. Balatsky, Phys. Rev. Lett. 95 , 057205 (2005)). Starting from a system with helical spin con- figuration, we solved for the forms of the electron wave functions and analyzed their characteristics. The relation between ferroelectricity and Dzyaloshinskii- Moriya interaction (I. Dzyaloshinskii, J. Phys. Chem. Solids 4 , 241 (1958) and T. Moriya, Phys. Rev. 120 , 91 (1960)) is clearly established. There is also a simple relation between the electric polarization and the wave vector of magnetic orders. Finally, we show that the bond-bending existing in transition metal oxides can enhance ferroelectricity. PACS: 75.80.+q, 77.80.-e 1 arXiv:0711.0100v2 [cond-mat.str-el] 28 Apr 2008