Stereoscopic Insight into Dilute Superconductivity of Perovskite Semiconductors

非技术性摘要在Bardeen、Cooper和Schrieffer提出第一个成功的超导理论几十年后，对某些材料中产生超导现象的物理机制的理解仍然具有挑战性。一些半导体材料在掺杂了很少的电子时成功地变成了超导，这与传统理论相矛盾。其中一种材料是钛酸锶，它是一种钙钛矿型氧化物，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电性，它的性质与钛酸锶相似，但不完全相同。这项研究项目比较了由钽酸钾和钛酸锶制成的纳米级器件的性能，以此来了解这两个系统的基本行为，包括超导电性的起源。这些器件是使用两种互补的方法制造的：(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纳米级的设备，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非凡性质的新型量子技术非常重要。该项目为各级学生提供了科研机会，特别是为STEM中传统上代表性不足的群体提供了科研机会。研究机会将专门提供给大学一年级或二年级的学生，希望其中一些人将在整个本科职业生涯和以后继续下去。科学指导最具挑战性的方面之一，特别是对代表不足的群体来说，是如何灌输一种“成长”的心态。最近在量子力学入门的高级课程中实施的一种“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。它对灌输增长思维的有效性将得到评估。技术摘要本研究项目探讨了钽酸钾(KTO)超导电性的微观起源。纳米器件是用KTO(110)和KTO(111)利用PI以前开发的技术来控制钛酸锶(STO)基异质结构的电导率和超导电性。该项目直接解决了一些重要问题，如：为什么KTO(111)和KTO(110)异质结具有超导电性，而KTO(100)不具有超导电性？KTO超导电性是否与近表面结构相变有关？KTO是否表现出超导体制(如STO)之外的电子配对的特征？自旋-轨道耦合的作用是什么？这一研究项目提供的关于KTO的“立体”洞察力，与现有的关于STO的最新知识基础相结合，将有助于准确地确定KTO和STO的哪些共同属性合谋在极低密度下产生超导行为。对共享机制的更深入理解可能会导致更高温度的类似物，或者只是帮助提供对某一材料家族的更深层次理解，这些材料有朝一日可能被用于未来的量子技术。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.