Multi-Mode RF Electron Pulse Compression for Ultrafast Electron Scattering

目前，全世界正在进行一项巨大的努力，致力于开发和应用新的实验方法，使直接观察物质的时间演变结构成为可能。这些方法结合了最先进的飞秒激光(见2018年诺贝尔物理学奖)和超短X射线或电子脉冲源，以获取时间分辨的衍射/散射图案和图像。如果时间分辨率接近~10飞秒--分子和材料中最高频率振动的时间尺度--原子运动在观察期间基本上是冻结的，人们可以完全遵循基本动力学来制作“分子电影”；这是分子动力学模拟的实验等价物。可以观察化学键的断裂/形成并直接确定复杂反应的过渡态结构，遵循相变动力学揭示材料结构和性质之间的深层联系，并直接观察电荷、轨道和晶格自由度在时间和动量上的耦合。 这项提议的重点是进一步开发世界上最强大的超快电子散射仪，该仪器由麦吉尔大学设计、建造和运行。我们需要的设备是在我们以前成功的基础上建立起来的，并能够以前所未有的时间分辨率约50飞秒进行超快电子散射。这一新能力将开辟一个巨大的有待探索的新“科学空间”。有了所需的设备，我们希望能够为半导体和金属中的超导、电荷密度波、热电、光伏和载流子迁移率等各种材料现象提供新的线索。我们将能够研究一系列强关联材料(过渡金属氧化物、焦绿石氧化物、锰氧化物和铜酸盐)中强多轨道电子关联、结构扭曲、电荷和轨道有序之间的复杂相互作用，以及这些系统中准粒子的形成动力学。此外，还有可能发现新的光诱导相和使用所建议的工具对复杂材料进行光学控制的途径；这是材料研究的前沿课题。

There is currently an enormous, worldwide effort directed at the development and application of new experimental methods that make it possible to directly watch' the time evolving structure of matter. These approaches combine state-of-the-art femtosecond lasers (see Nobel Prize in Physics, 2018) and sources of either ultrashort Xray or electron pulses to acquire time-resolved diffraction/scattering patterns and images. If time-resolution approaches ~10 femtoseconds - the timescale of the highest frequency vibrations in molecules and materials - atomic motion is essentially frozen during an observation and one can completely follow the fundamental dynamics to produce a "molecular movie"; the experimental equivalent of a molecular dynamics simulation. It is possible to watch chemical bonds break/form and directly determine transition-state structures for even complex reactions, to follow phase transition dynamics uncovering the deep connections between the structure and properties of materials, and directly observe the coupling between charge, orbital and lattice degrees of freedom in time and momentum. This proposal is focused on the further development of the World's most powerful ultrafast electron scattering instrument, designed, built and operating at McGill University. We are requesting equipment that builds on our previous successes and enables ultrafast electron scattering at an unprecedented time resolution of ~50 fs. This new capability will open up an enormous new 'scientific space' to be explored. With the requested equipment, we expect to be able to shed new light on materials phenomena as diverse as superconductivity, charge density waves, thermoelectricity, photovoltaicity and carrier mobility in semiconductors and metals. We will be in a position to investigate the complex interplay between strong, multiorbital electronic correlations, structural distortions, charge and orbital order across a range of strongly correlated material where this physics determines properties (transition metal oxides, pyrochlore oxides, manganites and cuprates), and the formation dynamics of quasiparticles in these systems. Further, there is also the possibility of discovering new photoinduced phases and avenues for optical control of complex materials using the proposed tools; a topic at the forefront of materials research.