Zhang, J. X., He, Q., Trassin, M., Luo, W., Yi, D., Rossell, M. D., et al. (2011). Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-like BiFeO3. Physical Review Letters, 107(14): 147602, pp. 147602-1-147602-5. doi:10.1103/PhysRevLett.107.147602.