MRI: Acquisition of Helium Recovery Equipment For Time-Resolved ARPES at NSF-NeXUS

该MRI奖项资助在NSF-NeXUS（国家极端超快科学）中型设施中购买超低温冰箱，用于将样品冷却到10开尔文（-440华氏度，-260摄氏度）的温度，NSF-NeXUS是俄亥俄州州立大学的开放式超快激光用户设施。量子材料中许多最有趣的现象都发生在这些非常低的温度下，因此这是实现广泛实验的关键组成部分。该项目汇集了一批二维材料，手性材料，磁性材料和拓扑材料的领先科学家，他们是首批实验和初始用户群的一部分。教育和推广活动强调这些先进的仪器，它们的科学价值，以及对观众的社会影响，从相邻学科的研究人员到研究生和本科生。这项研究的目标是了解量子材料中电子波的动力学，这可能会导致更快，更节能的电子和先进的量子技术。这是通过新开发的实验技术实现的，这些技术直接在NeXUS中型设施中对时间，空间，能量和动量的电子动力学进行成像。动量显微镜（MM）和高次谐波产生光源的使用通过增加空间分辨率（~2微米）和全布里渊区映射，在时间分辨、角度分辨光电子能谱（TR-ARPES）方面取得了重大进展。这使得在各种有趣的量子材料，包括二维材料（过渡金属二硫属化物，石墨烯，扭曲莫尔异质结构等），远离伽马点的狄拉克锥的拓扑材料，以及自旋电子学的手性和磁性材料中的载流子，激子和带结构动力学的泵浦-探测研究成为可能。该项目的研究人员正在利用基于MM的TR-ARPES的综合能量，动量，空间和时间分辨率来研究和理解激子弛豫过程，异质结构中的电荷转移，谷动力学和相关基态，以及光诱导相变和能带结构和Berry曲率的动态操纵。在NeXUS TR-ARPES光束线上增加新的闭合循环制冷机，可以将样品温度系统地变化到10 K，这对于研究量子材料的奇异相以及了解声子在动力学中的作用至关重要。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。

This MRI award funds the acquisition of an ultralow temperature refrigerator for cooling samples down to a temperature of 10 Kelvin (-440 degrees F, -260 degrees C) at the NSF-NeXUS (National Extreme Ultrafast Science) mid-scale facility, an open-access ultrafast laser user facility at the Ohio State University. Many of the most interesting phenomena in quantum materials occur at these very low temperatures, so this is a critical component for enabling a broad range of experiments. This project brings together a group of leading scientists in two-dimensional materials, chiral materials, magnetic materials, and topological materials, who are part of the first experiments and initial user base. Education and outreach activities highlight these advanced instruments, their scientific value, and societal impacts to audiences ranging from researchers in adjacent disciplines to graduate and undergraduate students.The goal of this research is to understand the dynamics of electron waves in quantum materials, which could lead to faster and more energy-efficient electronics and advanced quantum technologies. This is enabled by newly developed experimental techniques that directly image electron dynamics in time, space, energy, and momentum at the NeXUS mid-scale facility. The use of momentum microscopy (MM) and high-harmonic generation light sources produces a major advance in time-resolved, angle-resolved photoemission spectroscopy (TR-ARPES) by adding spatial resolution (~2 microns) and full Brillouin zone mapping. This enables pump-probe studies of carrier, exciton, and band structure dynamics in a variety of interesting quantum materials including two-dimensional materials (transition metal dichalcogenides, graphene, twisted moiré heterostructures, etc), topological materials with Dirac cones away from the gamma point, and chiral and magnetic materials for spintronics. Researchers on this project are utilizing the combined energy-, momentum-, spatial- and temporal-resolution of MM-based TR-ARPES to investigate and understand exciton relaxation processes, charge transfer in heterostructures, valley dynamics, and correlated ground states, as well as light-induced phase transitions and the dynamic manipulation of band structures and Berry curvature. The addition of the new closed-cycle cryocooler to the NeXUS TR-ARPES beamline enables the systematic variation of sample temperature down to 10 K, which is critical for studying exotic phases of quantum materials and also understanding the role of phonons on the dynamics.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.