Stereoscopic Insight into Dilute Superconductivity of Perovskite Semiconductors

非技术性摘要理解某些材料中产生超导现象的物理机制仍然具有挑战性，即使是在Barthel，库珀和Schrieffer开发出第一个成功的超导理论的几十年后。一些半导体材料在掺杂很少的电子时就能变成超导体，这与传统的理论相矛盾。一种这样的材料，钛酸锶，一种钙钛矿氧化物，在1964年被证明是超导体。最近，在一种类似的化合物钽酸钾中发现了超导性，钽酸钾的性质与钛酸锶相似，但不完全相同。该研究计划比较了由钽酸钾制成的纳米级器件与由钛酸锶制成的器件的特性，以了解这两种系统的基本行为，包括超导性的起源。这些器件是使用两种互补的方法创建的：（1）导电原子力显微镜光刻，和（2）超低压电子束光刻。这两种技术都能够创造出纳米级的器件，其特性揭示了这些材料的基本方面以及它们为什么会这样做。由此产生的见解对于开发利用这些材料的显着特性的新型量子技术非常重要。该项目为各级学生提供科学研究机会，特别是传统上代表性不足的STEM群体。研究机会将专门提供给谁是在他们的第一或第二年在大学的学生，希望有些将继续在他们的本科生涯及以后。科学导师制最具挑战性的方面之一，特别是对代表性不足的群体，是如何灌输一种“成长”的心态。最近在量子力学入门高级课程中实施的“心态干预”方法将适用于在研究环境中工作的本科生和博士生。将评估其灌输成长心态的功效。技术摘要本研究计划探讨钽酸钾（KTO）超导性的微观起源。纳米级器件由KTO（110）和KTO（111）使用PI先前开发的技术创建，以控制钛酸锶（STO）基异质结构中的导电性和超导性。该项目直接解决了一些重要的问题，例如：为什么KTO（111）和KTO（110）异质结构表现出超导性，而KTO（100）却没有？KTO超导性与近表面结构相变有关吗？KTO是否表现出超导体系之外的电子配对特征（如STO）？自旋轨道耦合的作用是什么？该研究计划提供的“立体”洞察力集中在KTO上，当与现有的关于STO的最新知识基础相结合时，将有助于确定KTO和STO的哪些共同属性在极低密度下产生超导行为。更深入地了解一个可能共享的机制可能会导致更高温度的类似物，或者只是帮助提供一个家庭的材料，有一天可能会被利用为未来的量子技术的更深入的了解。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.