Dr Peggy Qi Zhang
Whilst often discussed as non-trivial phases of low-dimensional ferroelectrics, modulated polar phases such as the dipolar maze and the nano-bubble state have been appraised as essentially distinct. Here we emphasize their topological nature and show that these self-patterned polar states, but also additional mesophases such as the disconnected labyrinthine phase and the mixed bimeron-skyrmion phase, can be fathomed in their plurality through the unifying canvas of phase separation kinetics. Under compressive strain, varying the control parameter, i.e., the external electric field, conditions the nonequilibrium self-assembly of domains, and bridges nucleation and spinodal decomposition via the sequential onset of topological transitions.
The evolutive topology of these polar textures is driven by the (re) combination of the elementary topological defects, merons and antimerons, into a plethora of composite topological defects such as the fourfold junctions, the bimeron and the target skyrmion. Moreover, we demonstrate that these manipulable defects are stable at room temperature and feature enhanced functionalities, appealing for devising future topological based nanoelectronics.
About the presenter
One of the three inaugural Women in FLEET fellows, Dr Peggy (Qi) Zhang studies topological domains in ultrathin, ferroelectric materials, investigating nanoscale bubble domains and topological transitions as part of FLEET’s Research theme 1, working with Nagarajan Valanoor at UNSW.
Peggy characterises topological domains using piezoresponse force microscopy. The nanoscale ferroelectric domains she studies have topological domain structures of the smallest size so-far achieved. The rotated polarisation and enhanced electromechanical response of these domains, makes them a promising candidate for novel, low-energy memory devices. She also studies design and fabrication of nanoscale memory devices using e-beam lithography and e-beam evaporation.