Investigation of Nonequilibrium States and Photoinduced Transitions in Topological Superlattices

非技术性描述：该项目研究了用超短激光脉冲操纵量子材料的新方法，这可能对开发节能的未来技术产生重大影响。感兴趣的材料是由两种类型的复合氧化物的交替层组成的薄膜，所述复合氧化物表现出不同的电极化性质，但结构相似。所得薄膜具有高度周期性的偏振域图案，其典型尺寸在10纳米范围内。通过在材料上照射激光脉冲，研究人员动态地修改了这些图案的空间顺序。通过频闪测量研究这些图案的时间演变，其时间分辨率足够快以观察电子运动，从而提供了对图案形成的基本机制的理解。找到光学控制偏振模式的途径可能具有深远的应用。这些图案可以编码可以被光迅速改变的信息。与传统电子器件相比，这减少了所使用的能量，同时使非易失性存储器或计算设备中的切换速度快了许多数量级。该项目包括教育活动，旨在培养物理，化学和材料科学之间接口的下一代科学家和工程师。这些活动将与K-12学生，本科生和研究生，以及社区的其他成员参与，以促进STEM领域的多样性，并提供宝贵的培训机会。技术描述：本项目研究拓扑超晶格中的非平衡态和光致跃迁。研究了一种由钛酸锶和钛酸铅交替层组成的铁电/顺电异质结构（STO-PTO）。这些异质结表现出各种拓扑安排的局部电极化形成长期秩序的极涡和skyrmions接近平衡。虽然传统的调谐旋钮，如成分，应变和温度只影响近平衡特性，但超快激光技术的快速改进为动态操纵这些空间复杂的偏振特性提供了新的机会。超快泵探测计划的部分固有复杂的STO-PTO系统被用来调查的时间演变的平衡阶段和局部拓扑结构。新的实验工具，包括超快宽带极紫外吸收光谱（UBXAS）和极紫外二次谐波发生（XUV-SHG），被用来测量超晶格的有序参数，跟踪能量弛豫过程光激发后，并检测在界面上的实时邻近破缺对称态。超快电子显微镜（UEM）被应用到解开极性skyrmion秩序和长程有序的拓扑缺陷的影响的真实空间动力学。该项目为中尺度系统中的界面和缺陷介导的相关性提供了新的见解。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: This project investigates new ways of manipulating quantum materials with ultrashort laser pulses, which can have a significant impact on developing energy-efficient future technologies. The material of interest is a thin film made up of alternating layers of two types of complex oxides that exhibit different electric polarization properties but are structurally similar. The resulting thin film has a highly periodic pattern of polarization domains with typical sizes in the range of 10 nanometers. By shining laser pulses on the material, the investigators dynamically modify the spatial order of these patterns. Studying the temporal evolution of these patterns by stroboscopic measurements with a temporal resolution fast enough to observe electron movements provides an understanding of the underlying mechanisms of pattern formation. Finding routes to optically control polarization patterns could have far-reaching applications. These patterns can encode information that can be rapidly changed by light. This reduces the amount of energy used compared to conventional electronics while enabling many orders of magnitude faster switching in non-volatile memories or computation devices. This project includes educational activities aimed at training the next generation of scientists and engineers at the interface between physics, chemistry, and materials science. These activities will engage with K-12 students, undergraduate and graduate students, and other members of the community to promote diversity in STEM fields and provide valuable training opportunities.Technical description: This project investigates nonequilibrium states and photoinduced transitions in topological superlattices. The research focuses on a ferroelectric/paraelectric heterostructure composed of alternating strontium titanate and lead titanate layers (STO-PTO). These heterostructures exhibit a variety of topological arrangement of local electric polarization forming long-range orders of polar vortices and skyrmions near equilibrium. While traditional tuning knobs like composition, strain, and temperature only affect near-equilibrium properties, rapid improvements in ultrafast laser technology presents a new opportunity to dynamically manipulate these spatially-complex polarization properties. Ultrafast pump-probe schemes specific to parts of the intrinsically complex STO-PTO system is used to investigate the temporal evolution of out-of-equilibrium phases and local topology. Novel experimental tools, including ultrafast broadband extreme-ultraviolet absorption spectroscopy (UBXAS) and extreme ultraviolet second harmonic generation (XUV-SHG), are used to measure superlattice order parameters, trace energetic relaxation processes following photoexcitation, and detect proximitized broken-symmetry states at the interface in real-time. Ultrafast electron microscopy (UEM) is applied to unravel real-space dynamics of the polar skyrmion order and the impact of topological defects on long-range order. The project provides novel insights into interface and defect-mediated correlations in mesoscale systems.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.