CAREER: Engineering artificial oxide layers with hidden spin symmetry for drivable 2D quantum magnetism

非技术摘要：从人类历史的远古时代起，磁性材料就已为人所知，并被开发应用。虽然它们在现代的高级用途在计算机和电子产品中很常见，但新的磁性材料对于开发安全性更好、速度更快、体积更小的下一代处理器、存储器和传感器是必要的。二维量子反铁磁体具有这样的前景，因为它以原子层的形式具有高度的可扩展性。然而，与铁磁体不同的是，反铁磁体本质上抵抗磁场的控制。此外，实现二维磁体是非常具有挑战性的，因为真正的材料是三维的。为了克服这些困难，有必要通过原子精度的设计来发展材料合成的能力。本研究的重点是氧化物材料的原子分层，以实现量子反铁磁体，不仅是二维的，而且是外部可控的。具体地说，Ir基氧化物被用来实现这样一种设计，即反铁磁体保持其内部磁结构，但仍以类似于铁磁体的方式响应磁场。该项目涉及对本科物理课程教材的修改，以及一个专门针对未被充分代表的少数群体和普通公众的推广部分。技术摘要：实现对二维量子海森堡反铁磁体的控制不仅增进了我们对量子多体物理的理解，而且使我们能够利用量子效应来开发新技术。然而，实现有效的外部控制是非常具有挑战性的，因为外部磁场与反铁磁秩序不存在直接的线性耦合。此外，在实际材料中，内部自旋各向异性和三维耦合总是存在的，从而抑制了二维临界涨落。虽然这些障碍在块状材料中很难克服，但主要研究人员计划使用现场监控的脉冲激光沉积生长来构建各种原子薄的外延氧化层，这些氧化层具有强烈的自旋-轨道耦合，产生巨大的各向异性交换作用和自旋倾斜，但保持自旋旋转对称性。由此产生的二维量子反铁磁晶格有望接近自旋各向同性极限，并对外加电场表现出良好的响应。这种独特的机制可以通过外延生长改变氧化层的厚度、结构扭曲、成分和应变状态来实现。一个重要的目标是揭示量子相变附近的二维临界涨落，并通过一系列表征技术建立反铁磁序参数的外部控制，包括先进的同步X射线散射和光谱。这一结果有望促进功能性二维量子反铁磁体的开发。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。

Nontechnical abstract: Magnetic materials have been known and exploited for applications since the ancient times of human history. While their advanced use in modern days can be commonly found in computers and electronics, new magnetic materials are necessary for developing a next generation of processors, memories, and sensors with better security, faster speed, and smaller size. Two-dimensional quantum antiferromagnet holds such promise because of its high scalability in the form of atomic layers. However, antiferromagnets, unlike ferromagnets, intrinsically resist control with a magnetic field. Moreover, realizing two-dimensional magnets is highly challenging because real materials are three dimensional. To overcome these difficulties, it is necessary to develop the capability of material synthesis by design with atomic precision. This research focuses on atomic layering of oxide materials to achieve quantum antiferromagnets that are not only two-dimensional but also externally controllable. Specifically, iridium-based oxides are used to realize a design where the antiferromagnet retains its internal magnetic structure and yet responds to magnetic field in a way similar to a ferromagnet. The project involves a revamp of undergraduate physics course materials, along with an outreach component that specifically targets underrepresented minorities and the general public.Technical abstract: Achieving control of two-dimensional quantum Heisenberg antiferromagnets is not only advancing our understanding of quantum many-body physics but also enables exploitation of quantum effects for new technologies. Realizing efficient external control is however highly challenging because of no direct linear coupling of an external magnetic field to the antiferromagnetic order. Moreover, internal spin anisotropy and three-dimensional coupling are always present in real materials, suppressing the two-dimensional critical fluctuations. While these barriers are difficult to overcome in bulk materials, the principle investigator plans to employ in-situ-monitored pulsed-laser deposition growth to construct a variety of atomically thin epitaxial oxide layers with strong spin-orbit coupling that creates large anisotropic exchange interactions and spin canting but preserves the spin rotational symmetry. The resulting two-dimensional quantum antiferromagnetic lattices is expected to be in close proximity to the spin isotropic limit and exhibits iant responses to applied external fields. This unique mechanism can be implemented by engineering the thicknesses, structural distortions, composition, and strain state of the oxide layers through epitaxial growth. An important goal is to unveil the two-dimensional critical fluctuations near quantum phase transitions, and to establish external controls of the antiferromagnetic order parameter via a suite of characterization techniques, including advanced synchrotron x-ray scattering and spectroscopy. The results are expected to facilitate the development of functional two-dimensional quantum antiferromagnets.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.