Novel measures of thermalization and time-evolution of strongly correlated, disordered, and topological systems by nonlinear THz spectroscopy

非技术摘要：如果一个物理系统受到震动，它恢复平衡的速度是衡量其物理特性的一个重要指标。在材料中，我们习惯于根据它们对小电场和磁场的响应来测量这样的速率。例如，在电场脉冲作用下，金属中电流的衰减率可以与其光学导电性中低频“德鲁德”响应的宽度有关。极化衰减的速率对应于德拜弛豫泛函形式中宽峰的宽度。相比之下，能量弛豫率是支配许多过程的基本速率，但不幸的是，它不能通过使用小场的传统电动力学测量直接测量。这项建议涉及开发测量工具，以探测具有大太赫兹范围场的材料，这些材料可以将材料推向远离平衡的位置，从而允许测量新的参数。在这个提议中，感兴趣的系统具有关于它们的相互作用或能带结构的非常规特征，这将以有趣的方式影响能量弛豫。该团队将研究具有有趣的量子力学关联的各种材料中的能量弛豫速率。该项目还包括一项广泛的教育和外联倡议。这项工作在培养具有独特技能的学生方面具有特别的教育价值，为他们成为高科技行业的劳动力做好准备。研究团队将在约翰·霍普金斯物理博览会中发挥积极作用-这是一项外联活动，每年在周六的活动中吸引数百人参观霍普金斯大学的实验室，并让他们接触到各种物理演示和活动。该团队还将在物理博览会上进行演示，并与资源不足的当地学校合作。技术摘要：这是一个项目，旨在利用新的非线性“泵浦-探测”太赫兹光谱仪研究强关联、拓扑和无序系统中能量弛豫、时间演化和热化的基本方面。研究小组将利用太赫兹范围2D相干光谱(及其相关技术)的最新发展，以获得关于相关金属和拓扑金属以及无序电子玻璃中的能量弛豫的新信息。测量将强调扩展的太赫兹范围(此处为0.1-40太赫兹[0.4-165兆赫])，在该范围内，响应通常针对低能量出射自由度，但实验将使用通过近红外向上的全部光子能量。太赫兹范围动力学和量子材料的非线性响应是一个有效的开放领域，人们对此很感兴趣，也有一些理论，但实验很少。在其他方面，该团队将研究铜酸盐超导体中“普朗克耗散”状态下的能量弛豫速率。有人推测，它们的反常性质反映了由最大允许的非弹性散射引起的驰豫速率的内在量子力学约束。这是从电阻率实验和其他实验中推断出来的。该团队将通过探索能量松弛与这个有边界的尺度之间的相互作用来阐明这一非凡特性的起源。另一个将面临凝聚态物理学长期挑战的项目是理解同时具有强相互作用和强无序的材料。该团队将研究3D金属-绝缘体转变的绝缘侧掺杂半导体的“电子-玻璃”状态下的热化和时间演化问题。该团队将同时使用太赫兹2D相干光谱和太赫兹泵浦探测光谱这两种新技术。在这类玻璃中，电子子系统内部和晶格耦合的能量弛豫机制预计将非常不同，这项研究的结果可能与多体局域系统中缺乏热化有关。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Abstract:If a physical system is shaken, the rate that it returns to equilibrium is an important measure of its physics. In materials, we are used to measuring such rates in the context of their response to small electric and magnetic fields. For instance, the rate that current decays in a metal after an electric field impulse can be related to the width of its low-frequency “Drude” response in its optical conductivity. The rate that polarization decays after polling a liquid with an electric field corresponds to the width of the broad peak in the Debye relaxational functional form. In contrast, the energy relaxation rate is a fundamental rate that governs many processes, but which is unfortunately not measured straightforwardly via conventional electrodynamic measurements using small fields. This proposal concerns the development of measurement tools to probe materials with large THz range fields that can push materials far from equilibrium allowing new parameters to be measured. The systems of interest in this proposal possess unconventional features with regards to their interactions or band structures that will affect energy relaxation in interesting ways. The team will investigate the rates of energy relaxation in a variety of materials with interesting quantum mechanical correlations. This project also includes a broad initiative in education and outreach. The work is of particular educational value in training students with unique skills to prepare them as the work force in high-tech industries. The research team will play active roles in the Johns Hopkins Physics Fair- an outreach activity which brings hundreds of people each year through Hopkins' labs during a Saturday event and exposes them to various physics demonstrations and activities. The team will also give demonstration shows at the Physics Fair and work with under-resourced local schools.Technical Abstract:This is a project to investigate fundamental aspects of energy relaxation, time-evolution, and thermalization in strongly correlated, topological, and disordered systems by new nonlinear “pump-probe” THz spectroscopies. The research team will exploit recent developments in the form of THz range 2D coherent spectroscopy (and its relatives) to get new information about energy relaxation in correlated and topological metals, as well as disordered electron glasses. Measurements will emphasize the extended THz range (here 0.1 - 40 THz [0.4 - 165 meV]) where generally responses target the low energy emergent degrees of freedom, but experiments will use a full complement of photon energies up through the near infrared. This topic of THz range dynamics and nonlinear response of quantum materials is an effectively wide-open area, in which there has been much interest and some theory, but very few experiments. Among other aspects, the team will investigate the rates of energy relaxation in the regime of “Plankian dissipation” in the cuprate superconductors. It has been conjectured that their anomalous properties reflect an intrinsic quantum mechanical bound on the rate of relaxation that arises from maximally allowed inelastic scattering. This has been inferred from the resistivity experiments, among others. The team will shed light on the origin of this remarkable property by probing the interplay of energy relaxation with this bounding scale. Another project that will confront a long-standing challenge in condensed matter physics is the understanding of materials with both strong interactions and strong disorder. The team will investigate the issue of thermalization and time-evolution in the “electron- glass” state of doped semiconductors on the insulating side of the 3D metal-insulator transition. The team will use both the novel technique of THz 2D coherent and THz pump-probe spectroscopy. The mechanism of energy relaxation, both internal to the electron sub-system and coupling to the lattice are expected to be very different in such glasses and the results of this study may have relevance to the lack of thermalization in many-body localized 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.