Ultrafast terahertz measurements of quantum dynamics in matter

相关的电子和量子材料在高效能量收集装置中得到应用，从光电学和热电学到低功率电子学。然而，材料科学只是触及了它们潜力的表面，深入了解它们的特性仍然是一个重大挑战。电荷、晶格、轨道和自旋自由度之间的复杂相互作用使其丰富的性质在微观层面上难以理解。这些相互作用的自然能量尺度通常在太赫兹（THz）区域，时间分辨的THz技术是通过观察光学扰动后出现的相位动态展开来解开这种复杂性的有力工具。我的研究计划的长期目标是开发和应用新的时间分辨太赫兹技术来探测物质的量子动力学，并了解与能量收集应用相关的紧急属性的起源。当前感兴趣的材料是显示出高热电性能的金属单硫族化物。我们采取三种不同的方法来实现这一目标，这些方法可以在短期内完成：第一种是使用时间分辨的超宽带THz光谱来观察准粒子的量子动力学，因为它们出生，观察电荷和晶格之间的相关性和相互作用。我们最近使用这项研究的绝缘体到金属的转变VO 2和观察极化子相干量子拍频的混合金属卤化物钙钛矿。我们将探索热电，准二维金属monocalcohalcogenides表现出电子晶体，但声子玻璃的性质，与强电子-声子耦合和拓扑结构的元素取决于相位。第二个扩展了我们最近的工作超快电子脉冲从金属纳米尖驱动的高场，单光周期太赫兹光脉冲。在此基础上，我们正在开发一种超快点投影电子显微镜与电子束团电荷兼容的飞秒时间和纳米长度尺度上的单次拍摄成像。该系统具有接近原子分辨率的无像差，振动不敏感的电子显微镜的潜力，并且非常适合表征二维量子材料中的结构动力学和电荷再分布。 第三种方法是将定制的太赫兹光脉冲应用于旨在直接操纵序参数的新型量子控制实验。我的团队最近展示了一种新技术，可以任意控制THz光脉冲的时间电场分布。由于这种方法与新的高场太赫兹产生技术兼容，我们现在可以第一次在量子材料上进行多脉冲，复杂波形的太赫兹实验。这些将被应用于探索通过工程光物质相互作用对材料进行量子控制的新概念。

Correlated electron and quantum materials are finding applications in high efficiency energy harvesting devices, from photovoltaics and thermoelectrics to low power electronics. Material science has only scratched the surface of their potential, however, and a deep understanding of their properties remains a major challenge. The complex interplay between the charge, lattice, orbital and spin degrees of freedom underlying their rich properties makes a microscopic level understanding difficult on all fronts. The natural energy scale of these interactions is often in the terahertz (THz) region, and time-resolved THz techniques are powerful tools to disentangle this complexity by watching emergent phases dynamically unfold following optical perturbation. The long-term goal of my research program is to develop and apply new time-resolved THz techniques to probe the quantum dynamics of matter and understand the origin of emergent properties relevant for energy harvesting applications. Current materials of interest are the metal monochalcogenides showing high thermoelectric performance. We take three distinct approaches to this effort that can be accomplished in the short term: The first is to use time-resolved ultrabroadband THz spectroscopy to observe the quantum kinetics of quasiparticles as they are born, watching as correlations and interactions develop between charge and lattice. We have recently used this study the insulator-to-metal transitions in VO2 and to observe polaron coherent quantum beats in the hybrid metal halide perovskites. We will explore the thermoelectric, quasi-2D metal monochalcogenides exhibiting electron crystal but a phonon glass properties, with elements of strong electron-phonon coupling and topology depending on the phase. The second extends our recent work on ultrafast electron pulses from a metal nanotip driven by high field, single optical cycle THz light pulses. Based on this, we are developing an ultrafast point-projection electron microscope with electron bunch charges compatible with single-shot imaging on femtosecond time and nm length scales. This system holds the potential for aberration-free, vibration-insensitive electron microscopy approaching atomic resolution and will be ideally suited to characterize structural dynamics and charge redistribution in 2D quantum materials. The third approach is in the application of tailored THz light pulses for novel quantum control experiments aimed at manipulating order parameters directly. My group recently demonstrated a new technique to arbitrarily control the temporal electric field profile of THz light pulses. As this method is compatible with new high field THz generation techniques, we can now do multi-pulse, complex waveform THz experiments on quantum materials for the first time. These will be applied to explore a new concept of quantum control over materials by engineered light-matter interactions.