Exotic Quantum Responses in Complex Oxide Thin Films

非技术性描述。该项目探索强关联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强烈耦合并共同响应外部刺激，从而提供超出传统半导体材料的响应。通过改进混合分子束外延法合成具有极低缺陷浓度的钒酸盐和钛酸盐薄膜，探索了这些超纯材料的电子性质。生长实验进行新提出的绝缘体BiVO 3和最终的四元化合物Bi 1-xSrxVO 3的合成膜。我们的目标是证明，电场控制电子性能可以在这些材料中实现。对应变薄膜的掺杂进行了探索，实验证实了利用外延应变可以诱导和提高超导转变温度。该研究预计将产生重大的科学和技术影响，通过提供对电子相变材料的全新见解，这些材料可用于传感器，高性能功率效率计算和量子计算的逻辑器件。该计划提供了多学科的培训机会，研究生和本科生在薄膜合成和电子相变材料的表征领域。推广活动针对K-12受众，培养他们对科学和技术的好奇心。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。生长实验的目的是映射条件，以访问一个自我调节的生长模式的三元氧化物化合物BiVO 3使用组合的生长方法，即传统的分子束外延和化学束外延。发展了一种BiVO 3自调节生长的生长策略，使四元化合物Bi 1-xSrxVO 3的薄膜合成成为可能。一个合作的研究方法是采取分析的四元系统，使用角分辨光电子能谱，透射电子显微镜，扫描隧道显微镜，和温度依赖的磁输运和非线性光学光谱。对固溶体Bi 1-xSrxVO 3的电子和光学性质的深入分析在强相关的钒酸盐材料系统中开辟了一个全新的设计空间，其中电场对带填充金属到绝缘体转变的量子临界点附近的电子性质的控制是固有的。详细的施主掺杂的应变量子顺电SrTiO 3和CaTiO 3的研究进行探索是否可以在CaTiO 3中诱导超导相，如果在SrTiO 3的超导转变温度可以提高，如果量子临界行为是稳定在较高的温度下使用外延应变。该项目的首要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，并了解其奇异响应。该奖项反映了NSF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.