Figure 1. Domain-shape-preserving DW breathing motion.

a-j, Successive out-of-plane PFM phase (θ) images of FE domains taken upon application of each pulse field. Domains expand and shrink in approximately the same patterns under the 1^st, 2^nd, 3^rd, 4^th, and 5^th series of negative (a, c, e, g, and i) and positive (b, d, f, h, and j) switching pulses with the respective switching times of τ_i and ξ_i (i = 1,2,3,4,5), τ_i and ξ_i are the cumulative pulse time of each domain-switching with negative and positive switching pulses, respectively, i.e. the sum of the widths of a series of switching pulses (Supplementary Fig. S3a). ⊙ and ⊗ represent the direction of the external upward and downward electric fields induced by negative and positive switching pulses, respectively. The bright and dark regions in the out-of-plane PFM images represent ferroelectric domains with up and down polarization, respectively.