MSE Special Speaker: Dr. Salva Salmani-Rezaie, University of California, Santa Barbara

Atomic Scale Understanding of Ferroelectricity and Superconductivity in SrTiO₃

SrTiO₃ is an incipient ferroelectric, and the first oxide superconductor discovered. The nature of ferroelectric and superconducting transitions, however, is still heavily debated. In this talk, I report on the atomic-scale mechanisms of how SrTiO₃ transforms into a ferroelectric state using epitaxial strain. Using HAADF-STEM and analyzing Ti columns off-centering, I show local polar regions above the Curie temperature, highlighting the order-disorder nature of the ferroelectric transition in SrTiO₃. Next, I focus on understanding the competition between mobile charge carriers and correlated polar distortions. Elucidating the nature of this competition is of interest for the last part of this talk which focuses on the nature of superconductivity in SrTiO₃. Using STEM imaging, I find that the superconducting critical temperature is directly proportional to the correlation length of polar distortions. If the polar nanodomains are sufficiently large, the Cooper pairs experience a non-centrosymmetric lattice with spin-orbit coupling. I report a doubling in critical temperature of superconductivity when the polar nanodomains are larger than the coherence length of Cooper pairs.

Bio

I have recently obtained my Ph.D. in material science with Professor Susanne Stemmer at the University of California, Santa Barbara. I use transmission electron microscopy and microanalysis to reveal the fundamental properties of quantum materials. My primary research is focused on recognizing the role of intertwined orders in quantum materials to understand emergent quantum phenomena like topological superconductivity. Recently I studied the nature of ferroelectricity in SrTiO3 and how polar instabilities in atomic-scale enhance superconductivity in this material. These findings help with explaining the mechanism of superconductivity in SrTiO3. I am also interested in understanding the role of defects on the properties of quantum materials and tuning defects to be beneficial. I have been awarded a Kavli postdoctoral fellowship from the Kavli Institute at Cornell University and joined Professor David Muller’s group end of September 2021.

Zoom option:

https://osu.zoom.us/j/91540876010?pwd=Z2RRa2FHUWdYdkphUGhDcjlUVzdPdz09

Meeting ID: 915 4087 6010

Password: 879628