Multiscale electric-field imaging of polarization vortex structures in PbTiO3/SrTiO3 superlattices oleh Christopher Addiego, Jacob A. Zorn, Wenpei Gao, Sujit Das, Jiaqi Guo, Chengqing Qu, Liming Zhao, Lane W. Martin, Ramamoorthy Ramesh, Long-Qing Chen, Xiaoqing Pan