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Tunable Nanoscale Evolution and Topological Phase Transitions of a Polar Vortex Supercrystal.

  • Author(s): Dai, Cheng;
  • Stoica, Vladimir Alexandru;
  • Das, Sujit;
  • Hong, Zijian;
  • Martin, Lane W;
  • Ramesh, Ramamoorthy;
  • Freeland, John W;
  • Wen, Haidan;
  • Gopalan, Venkatraman;
  • Chen, Long-Qing
  • et al.
Abstract

Understanding the phase transitions and domain evolutions of mesoscale topological structures in ferroic materials is critical to realizing their potential applications in next-generation high-performance storage devices. Here, the behaviors of a mesoscale supercrystal are studied with 3D nanoscale periodicity and rotational topology phases in a PbTiO3 /SrTiO3 (PTO/STO) superlattice under thermal and electrical stimuli using a combination of phase-field simulations and X-ray diffraction experiments. A phase diagram of temperature versus polar state is constructed, showing the formation of the supercrystal from a mixed vortex and a-twin state and a temperature-dependent erasing process of a supercrystal returning to a classical a-twin structure. Under an in-plane electric field bias at room temperature, the vortex topology of the supercrystal irreversibly transforms to a new type of stripe-like supercrystal. Under an out-of-plane electric field, the vortices inside the supercrystal undergo a topological phase transition to polar skyrmions. These results demonstrate the potential for the on-demand manipulation of polar topology and transformations in supercrystals using electric fields. The findings provide a theoretical understanding that may be utilized to guide the design and control of mesoscale polar structures and to explore novel polar structures in other systems and their topological nature.

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