Exotic Quantum Responses in Complex Oxide Thin Films

非技术性的描述。该项目探索强相关电子系统的内在电子和光学性质。与目前用于信息技术的半导体不同，这些材料系统中的电子是强耦合的，并且集体响应外部刺激，从而提供超出传统半导体材料的响应。通过杂化分子束外延技术的改进，合成了缺陷浓度极低的钒酸盐和钛酸盐薄膜，研究了这些超纯材料的电子性能。通过生长实验合成了新提出的绝缘体BiVO3薄膜，并最终合成了季元化合物Bi1-xSrxVO3。目标是证明电场对电子特性的控制可以在这些材料中实现。通过实验验证了利用外延应变可以诱导和提高薄膜的超导转变温度。这项研究预计将产生重大的科学和技术影响，为电子相变材料提供新的见解，这些材料可用于传感器、用于高性能节能计算的逻辑器件和量子计算。该计划为薄膜合成和电子相变材料表征领域的研究生和本科生提供多学科培训机会。外展活动以K-12学生为对象，培养他们对科学技术的好奇心。技术描述。该项目侧重于与钙钛矿结构复合氧化物薄膜合成相关的生长动力学基础研究。生长实验旨在通过常规分子束外延和化学束外延的组合生长方法，绘制条件以获得BiVO3三元氧化物化合物的自我调节生长模式。研究了BiVO3的生长策略，实现了Bi1-xSrxVO3的薄膜合成。采用角度分辨光谱学、透射电子显微镜、扫描隧道显微镜、温度相关磁输运和非线性光谱学等方法对四元体系进行了分析。深入分析固溶体Bi1-xSrxVO3的电子和光学性质，为强相关钒酸盐材料体系开辟了一个全新的设计空间，在强相关钒酸盐材料体系中，电场控制在带填充金属到绝缘体过渡的量子临界点附近的电子性质是固有的。对应变量子准电SrTiO3和CaTiO3进行了详细的供体掺杂研究，以探索CaTiO3中是否可以诱导超导相，以及如果使用外延应变在更高温度下稳定量子临界行为，SrTiO3中的超导转变温度是否可以提高。该项目的总体目标是探索复杂氧化物中表现出强电子相关效应的新量子相，并了解它们的奇异反应。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical description. The project explores the intrinsic electronic and optical properties in strongly correlated electron systems. Unlike in semiconductors, which are currently utilized in information technology, electrons in these material systems are strongly coupled and collectively respond to external stimuli, thus offering responses that are beyond conventional semiconductor materials. Enabled by the improvement to synthesize vanadate and titanate thin films with exceptionally low defect concentration by hybrid molecular beam epitaxy the electronic properties of these ultrapure materials are explored. Growth experiments are performed to synthesize films of the newly proposed insulator BiVO3 and ultimately the quaternary compound Bi1-xSrxVO3. The goal is to demonstrate that electric field control over electronic properties can be realized in these materials. The doping of the strained thin films is explored to experimentally confirm that the superconducting transition temperature can be induced and enhanced by utilizing epitaxial strain. The research is expected to have significant scientific and technological impact, by providing fundamentally new insights into electronic phase transition materials that can be used in sensors, logic devices for high performance power efficient computing, and quantum computation. The program provides multidisciplinary training opportunities to graduate and undergraduate students in the area of thin film synthesis and characterization of electronic phase transition materials. Outreach activities target K-12 audiences to nurture their curiosity in science and technology.Technical description. The project focuses on fundamental studies of growth kinetics relevant to the synthesis of complex oxide thin films with perovskite structure. Growth experiments aim to map conditions to access a self-regulated growth mode for the ternary oxide compounds BiVO3 using a combinatorial growth approach, i.e. conventional molecular beam epitaxy and chemical beam epitaxy. A growth strategy is developed for the self-regulated growth of BiVO3, which enables the thin film synthesis of the quaternary compound Bi1-xSrxVO3. A collaborative research approach is taken to analyze the quaternary system using angle resolved photoemission spectroscopy, transmission electron microscopy, scanning tunneling microscopy, and temperature dependent magnetotransport and nonlinear optical spectroscopy. The in-depth analysis of electronic and optical properties of the solid solution Bi1-xSrxVO3 opens up an entirely new design space in the strongly correlated vanadate material system, in which electric field control over electronic properties near the quantum critical point of the band-filled metal-to-insulator transition is inherently built-in. Detailed donor doping studies of the strained quantum paraelectric SrTiO3 and CaTiO3 are conducted to explore whether a superconducting phase can be induced in CaTiO3, and if the superconducting transition temperatures in SrTiO3 can be enhanced if the quantum critical behavior is stabilized at higher temperature using epitaxial strain. The overarching goal of the project is to explore new quantum phases in complex oxides exhibiting strong electron correlation effects and to understand their exotic responses.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.