CAREER: Hidden Topological Polar Phases Created by Ultrafast Acoustic Excitation

NONTECHNICAL SUMMARY This award supports integrated research, educational, and outreach activities to advance the fundamental understanding of novel phases with complex polarization patterns in ferroelectrics. Ferroelectrics are materials that have orderly polarization (composed of pairs of equal and oppositely charged poles separated by a tiny distance) that can be manipulated by external fields. One of the exciting research areas in ferroelectrics is creating unconventional patterns of polarization, such as a polar vortex, where the swirling polarization can induce exotic fundamental phenomena and provide new opportunities for potential device applications such as ultrahigh-density vortex-based memory. However, such complex polar phases have so far been observed in only a few ferroelectric materials and mostly form spontaneously during materials synthesis. In this project, the PI and his research team will computationally demonstrate a radically new approach towards an on-demand creation of complex polar phases in ferroelectric materials. This new approach combines heterostructure design (integrating ferroelectric thin films with dissimilar materials) and the excitation by picosecond (one trillionth of a second) ultrasonic pulses. A new computer model will be developed to identify the materials, film thickness, duration and amplitude of the ultrasonic pulse, and other relevant parameters needed for the new complex polar phase creation, thereby providing guidance for both heterostructure synthesis and ultrafast control experiments. The research activities are integrated with educational and outreach activities which aim to develop, implement, assess, and disseminate a series of classroom modules focused on material structures seen at the micro level (called microstructures) for middle school and high school science education. The classroom modules will involve synergistic activities of microstructure modeling, 3D printing, and mechanical properties testing. The modules will be collaboratively developed by two secondary-school teachers, an education software company, a graduate student, and the PI. The modules will be tested in middle and high schools covering diverse student population, improved based on assessment results, and broadly disseminated to secondary schools in Wisconsin by organizing a teachers’ workshop and presentations at an educational conference, such that the modules can be used to engage and inspire hundreds and potentially thousands of secondary school students. TECHNICAL SUMMARY This award supports integrated research, educational, and outreach activities to advance the fundamental understanding of the formation of topological polar phases (e.g., vortices, skyrmions, merons) in ferroelectrics. Due to the strong gradient of polarization, topological polar phases can induce exotic fundamental phenomena and open new modalities for potential device applications. However, topological polar phases have so far been observed in only a few ferroelectric heterostructures and mostly form under equilibrium conditions. Ultrafast excitation is one promising approach to create long-lived nonequilibrium hidden phases of matter with emergent functionalities. The main objective of this research is to computationally create hidden topological polar phases in ferroelectric heterostructures by ultrafast acoustic excitation. To achieve this, the PI and his research team will develop a new mesoscale model that can accurately and rapidly predict the coupled dynamics of strain, polarization, and electromagnetic waves that will emerge in ferroelectric heterostructures after the injection of an ultrafast acoustic pulse. The model will then be utilized to predict and understand the formation of the initial polar phases under equilibrium condition and the final hidden polar phases upon ultrafast acoustic excitation. The research activities are integrated with educational and outreach activities which aim to develop, implement, assess, and disseminate a series of classroom modules focused on materials microstructures for middle school and high school science education. The classroom modules will involve synergistic activities of microstructure modeling, 3D printing, and mechanical properties testing. The modules will be collaboratively developed by two secondary-school teachers, an education software company, a graduate student, and the PI. The modules will be tested in middle and high schools covering diverse student population, improved based on assessment results, and broadly disseminated to secondary schools in Wisconsin by organizing a teachers’ workshop and presentations at an educational conference, such that the modules can be used to engage and inspire hundreds and potentially thousands of secondary school students. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.