Ultrafast Electron Scattering at Low Temperatures

目前有一个巨大的，世界范围内的努力，旨在发展和应用新的实验方法，使人们有可能直接“观察”的时间演变的物质结构。 这些方法结合了联合收割机最先进的飞秒激光器（参见2018年诺贝尔物理学奖）和超短X射线或电子脉冲源，以获得时间分辨的衍射/散射图案和图像。 在这些仪器所能达到的最高时间分辨率下，原子运动在观察过程中基本上是冻结的，人们可以完全遵循基本动力学来产生“分子电影”;实验相当于分子动力学模拟。 可以观察化学键的断裂/形成，并直接确定甚至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，甚至通过这些方法获得对蛋白质功能的原子级理解。* 该提案的重点是进一步开发世界上最强大的超快电子散射仪器，该仪器由麦吉尔大学设计、建造和运行。我们正在请求建立在以前成功的基础上的设备，并在低温下实现超快电子散射。这种新的能力将开辟一个巨大的新的“科学空间”进行探索。 通过所要求的设备，我们希望能够对半导体和金属中的超导性、电荷密度波、热电性、光致发光性和载流子迁移率等各种材料现象进行新的研究。 我们将能够研究强多轨道电子相关性、结构扭曲、电荷和轨道顺序之间的复杂相互作用，这些相互作用跨越一系列强相关材料，这些材料的物理性质决定了这些材料的性质。（过渡金属氧化物、烧绿石氧化物、锰氧化物和铜氧化物），并且有可能发现新的光诱导相和用于复杂材料的光学控制的途径，材料研究的前沿课题。

There is currently an enormous, world-wide 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. At the highest time-resolution achievable in these instruments, 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 even to obtain an atomic-level understanding of protein function with these approaches. ***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 previous successes and enables ultrafast electron scattering at cryogenic temperatures. 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, multi-orbital 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 there is a possibility of discovering new photoinduced phases and avenues for optical control of complex materials, a topic at the forefront of materials research.