Stereoscopic Insight into Dilute Superconductivity of Perovskite Semiconductors

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Non-technical AbstractUnderstanding the physical mechanism that gives rise to the phenomenon of superconductivity in some materials remains challenging, even decades after the first successful theory of superconductivity was developed by Bardeen, Cooper, and Schrieffer. Some semiconducting materials manage to become superconducting when doped with very few electrons, contradicting conventional theory. One such material, strontium titanate, a perovskite oxide, was shown to be a superconductor in 1964. More recently, superconductivity was discovered in a similar compound, potassium tantalate, whose properties are similar, but not identical, to strontium titanate. This research program compares the properties of nanometer-scale devices fabricated from potassium tantalate with devices made from strontium titanate as a way to understand the fundamental behavior, including the origin of superconductivity, of both systems. These devices are created using two complementary approaches: (1) conductive atomic force microscope lithography, and (2) ultra-low-voltage electron-beam lithography. Both techniques are capable of creating nanometer-scale devices whose properties reveal fundamental aspects of these materials and why they behave the way they do. The resulting insights are important for developing novel quantum technologies that make use of the remarkable properties of these materials. The project provides scientific research opportunities available to students at all levels, especially to traditionally underrepresented groups in STEM. Research opportunities will specifically be provided to students who are in their first or second year in college in the hope that some will continue throughout their undergraduate career and beyond. One of the most challenging aspects of scientific mentorship, especially to underrepresented groups, is how to instill a “growth” mindset. A “mindset intervention” method recently implemented in an upper-level course in introductory quantum mechanics will be adapted to undergraduate and PhD students working in a research environment. Its efficacy for instilling a growth mindset will be assessed. Technical AbstractThis research project investigates the microscopic origin of superconductivity in potassium tantalate (KTO). Nanoscale devices are created with KTO(110) and KTO(111) using techniques previously developed by the PI to control conductivity and superconductivity in strontium titantate (STO)-based heterostructures. The project directly addresses important questions such as: Why do KTO(111) and KTO(110) heterostructures exhibit superconductivity while KTO(100) does not? Is KTO superconductivity associated with a near-surface structural phase transition? Does KTO exhibit signatures of electron pairing outside of the superconducting regime (like STO)? What is the role of spin-orbit coupling? The “stereoscopic” insight provided by this research program focused on KTO, when combined with an existing base of recent knowledge about STO, will help to pinpoint which shared properties of KTO and STO conspire to produce superconducting behavior at exceptionally low densities. A deeper understanding of a, presumably, shared mechanism may lead to higher-temperature analogues, or simply help provide a deeper understanding of a family of materials that may one day be exploited for future quantum technologies.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.