Hidden X: Using spatial and magnetic symmetries to guide first principles search of compounds with hidden quantum properties X

该奖项支持旨在发现具有新颖电子和磁性质的新材料的理论和计算研究和教育。抽象物理理论的验证和实用新技术的发展都依赖于对关键材料的识别，这些材料具有使这些应用成为可能的特定特性。这种特殊材料的发现在历史上要么是幸运的偶然事件，要么是爱迪生对许多例子进行了耗时的经验或计算搜索。然而，许多独特的物理效应从根本上来说不仅取决于特定的材料常数，还取决于与原子几何形状或电子自旋排列有关的关键对称条件。另一方面，教科书上的对称规则往往忽略了相关的可能性。在这个项目中，PI将搜索“隐藏效应X”，它指的是某些效应X可能存在的一般情况，即使名义对称显然不允许。例如，具有相同动量但相反自旋的电子态可能具有稍微不同的能量，通常在没有反转对称的晶体材料和/或当材料含有重元素时。在这个项目中，PI将寻找在某些特殊情况下，不同自旋电子发生轻微能量分裂的材料，如晶体具有全局反转对称，或材料仅包含轻元素，或全局晶格对称掩盖了较低的局部对称。最近，一些“打破教科书规则”的做法得到了实验验证。这项研究有望在实际材料中揭示和验证更多这样的可能性。本研究的主题有助于教育和培训学生和博士后，以引导转变为一个持久的、充满活力的、基础的研究社区，跨越学科界限，为材料科学和工程创造新的途径，造福社会。特别是，该奖项将支持基础凝聚态物理和材料理论领域的博士后研究助理的教育和培训。PI将与他所在机构的研究、教学和学习整合中心合作，鼓励博士后研究人员参与大学水平的教学，为他们未来的STEM教师职位做好准备。该奖项支持旨在发现具有新颖电子和磁性质的新材料的理论和计算研究和教育。特别地，PI将搜索“隐藏效应X”，它指的是效应X存在的一般情况，即使名义上的整体晶体对称性显然不允许它存在，或者使其成为可能的对称性是一个容易被忽视的局部对称性。该项目将重点关注三个这样的隐藏X类别，其中启用对称性是(i)局部实空间位置对称性，即使在全局中心对称的化合物中也能实现Rashba和Dresselhaus自旋分裂效应；或（ii）不寻常的自旋纹理模式，这是基于化合物的空间群对称性而意想不到的，因为它们是由特定波矢量的（较低）对称性决定的；或（iii）磁对称性。它在某些反铁磁体中产生了类似拉什巴的动量依赖自旋分裂，但与拉什巴效应不同的是，这种分裂甚至在没有相对论物理的情况下也会发生——比如在没有自旋轨道耦合的情况下。此外，PI将从理论上阐述使不同效应在同一化合物中共存的对称条件，如铁电性和Rashba效应；或Rashba效应和拓扑绝缘。对于这些隐藏的X类别，PI将(a)从理论上确定相关的启用意外对称性，(b)将它们用作材料选择过滤器，以识别此类效应的特定化合物实现，从而有利于未来的实验，以及(c)通过密度泛函理论计算原型材料的相关电子结构。该奖项还支持在基础凝聚态物理和材料理论领域的博士后研究助理的教育和培训。PI将与他所在机构的研究、教学和学习整合中心合作，鼓励博士后研究人员参与大学水平的教学，为他们未来的STEM教师职位做好准备。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 SUMMARYThis award supports theoretical and computational research and education aimed at discovering new materials with novel electronic and magnetic properties. The validation of abstract physical theories and the development of practical novel technologies both depend on the identification of critical materials that harbor specific properties enabling such applications. The discovery of such special materials has proceeded historically either by lucky accidents, or by time-intensive Edisonian empirical or computational search of many examples. Yet, many unique physical effects are fundamentally enabled not just by specific materials constants, but also by critical symmetry conditions pertaining to the pattern of atomic geometries or arrangement of electronic spins. Textbook symmetry rules, on the other hand, often overlook pertinent possibilities. In this project, the PI will search for “Hidden Effects X”, which refers to the general conditions where some effect X is possible even when the nominal symmetry would apparently disallow it. For example, electronic states with the same momentum but opposite spins can have slightly different energies typically in crystalline materials without inversion symmetry and/or when the material contains heavy elements. In this project, the PI will search for materials in which this slight energy splitting for electrons of different spins occurs under the unexcepted circumstances when the crystal has global inversion symmetry, or when the material contains only light elements, or when the global lattice symmetry conceals the lower local symmetry. A few of such ‘breaking of the textbook rules’ have recently been validated experimentally. This research is expected to reveal and validate many more such possibilities in real materials. The subject matter of this research is instrumental for educating and training students and postdocs to lead the transformation to a durable, vibrant, and fundamental research community that cuts across disciplinary boundaries and creates new ways for materials science and engineering to bring benefits to society. In particular, this award will support the education and training of a postdoctoral research associate in the areas of fundamental condensed matter physics and materials theory. The PI will work with the Center for the Integration of Research, Teaching, and Learning at his institution to encourage postdoctoral researchers to be involved in college-level teaching, preparing them for future STEM faculty positions.TECHNICAL SUMMARYThis award supports theoretical and computational research and education aimed at discovering new materials with novel electronic and magnetic properties. In particular, the PI will search for “Hidden Effects X”, which refers to the general conditions where effect X exists even when the nominal global crystalline symmetry would apparently disallow it, or that the enabling symmetry is an easily overlooked local symmetry. This project will focus on three such Hidden X categories, where the enabling symmetries are (i) local real-space site symmetries that enable the Rashba and Dresselhaus spin splitting effects even in globally centrosymmetric compounds, or (ii) unusual spin texture patterns, which are unexpected on the basis of the space group symmetry of the compound, as they are determined by the (lower) symmetry of the specific wavevector, or (iii) magnetic symmetry, which gives rise to a Rashba-like momentum dependent spin splitting in certain antiferromagnets, except that unlike the Rashba effect this can happen even without relativistic physics – such as in the absence of spin-orbit coupling. In addition, the PI will work to formulate theoretically the symmetry conditions enabling the coexistence of different effects in the same compound, such as ferroelectricity and Rashba effect; or Rashba effect and topological insulation. For these Hidden X categories, the PI will (a) determine theoretically the pertinent enabling unexpected symmetries, (b) use them as material selection filters to identify specific compound realizations of such effects, to the benefit of future experiments, and (c) calculate the relevant electronic structure of prototype materials via the Density Functional Theory. This award also supports the education and training of a postdoctoral research associate in the areas of fundamental condensed matter physics and materials theory. The PI will work with the Center for the Integration of Research, Teaching, and Learning at his institution to encourage postdoctoral researchers to be involved in college-level teaching, preparing them for future STEM faculty positions.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.