Understanding the formation of metastable polar supercrystals

Ultrafast stimuli can stabilize and control metastable states of matter inaccessible by equilibrium means. Establishing the spatiotemporal link between ultrafast excitation and metastability is crucial to understanding these phenomena. This talk will focus on superlattices of PbTiO₃ (PTO) and SrTiO₃ (STO) that host a variety of extended polar textures such as supercrystals, vortices, skyrmions, collectively dubbed polar supertextures. This talk will focus on the exploration of the formation of polar supercrystals [1], which is a highly ordered phase created via optical excitation of these PTO/STO heterostructures. Since the transition is irreversible, an understanding of the formation pathway, we needed to use the high intensity ultrafast X-ray pulses from a free electron laser to track the single-shot dynamics of polar supercrystal creation from ps to us timescales[2]. Together with dynamical phase field modeling, these results enabled tracking of the irreversible formation of this metastable polar supertexture and understanding of the creation process. This approach in general opens the possibility to track irreversible transitions in novel materials.

[1] Stoica, V. A. et al. Optical creation of a supercrystal with three-dimensional nanoscale periodicity. Nat. Mater. 18, 377 (2019).

[2] Stoica, V. A. et al. Non-equilibrium pathways to emergent polar supertextures. Nat. Mater. 23, 1394 (2024).