Ultrafast Dynamics of Iron-Based Superconductors

非技术摘要：最近发现的铁的高温超导电性开启了凝聚态物理的新纪元，极大地扩展了量子材料的研究。理解铁基超导体在飞微微秒和纳秒时间尺度上光-物质相互作用的基本原理有助于对高温超导起源的新认识。从技术角度来看，这一知识对于全固态光学系统在实验室外的革命性应用非常重要，因为它们坚固耐用、效率高、体积紧凑且易于维护。本研究的目的是获得关于铁基超导体中准粒子和非平衡相的暂态动力学、载流子的再分布和驰豫以及电子和结构有序的超快操纵的新信息。这方面的知识对于构建基于新颖光学现象的全光学器件以及制造能够在相对较高的温度(高于~20K)下工作的高速光电超导Q比特至关重要。该项目对加强对西班牙裔STEM研究生和本科生的跨学科高级培训具有重大的制度影响。这项研究活动融合了广泛的科学、推广和技术经验，大部分研究是学生/博士后培训的一部分，目的是了解他们在学术界和工业界的职业生涯。技术摘要：这个项目进行实验，以阐明铁基量子材料的非平衡相的演变，这对于理解光激发下超导的基本动力学过程至关重要。各种强大的飞秒激光泵浦-探测光谱技术被应用于创造和表征新的量子相、准粒子弛豫和电子-玻色子相互作用。超快光学方法提供了对固体中特定自由度的模拟和选择性探测，以便在晶格振动的时间尺度上可视化多维非平衡动力学，揭示自发破坏对称性的动力学，阐明光致超导态的抑制/创造的隐藏相和特征，并对超短时间尺度上的“缠绕”有序参数提供新的见解。在宽的长度和时间尺度上的非平衡动力学的实时成像可以提供关于自旋波函数在其上是相干的尺度的重要信息。为了回答与尺寸相关的量子材料动力学的基本问题，应用了一种新的时间和角度分辨的半球光散射方法。这项技术可视化了低温下散射光的角分布，以监测不同尺寸的颗粒/磁区中的瞬时非平衡过程。铁基超导外延薄膜的制造是基于项目期间开发的新的脉冲激光沉积协议。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。

Nontechnical abstract: Recent discovery of high-temperature superconductivity in iron pnictides has initiated a new era in condensed matter physics, significantly expanding quantum materials research. The understanding of fundamental principles of light-matter interaction in iron-based superconductors on femto- pico- and nanosecond time scales contributes to new insight into the origin of High-T superconductivity. From a technological point of view, this knowledge is important for revolutionary applications of all-solid-state optical systems outside the laboratory because of their ruggedness, efficiency, compact size and ease of maintenance. The goal of this research is to obtain new information about transient dynamics of quasiparticles and nonequilibrium phases, carrier redistribution and relaxation, and ultrafast manipulation of electronic and structural order in iron-based superconductors. This knowledge is critical to build all-optical devices based on novel optical phenomena, and to create high-speed optoelectronic superconducting Q-bits which can operate at relatively high temperatures, above ~20 K. This project has significant institutional impact enhancing interdisciplinary advanced-level training for graduate and undergraduate Hispanic STEM students and postdoctoral researchers. The research activity integrates a broad spectrum of scientific, outreach and technical experiences, and most of the research is the part of the student/postdoctoral training on their ways to careers in academia and industry.Technical abstract: This project pursues experiments to elucidate the evolution of nonequilibrium phases of iron-based quantum materials, which is critical for understanding of fundamental dynamical processes of superconductivity upon photoexcitation. A variety of powerful femtosecond laser pump-probe spectroscopy techniques are applied to create and characterize novel quantum phases, quasiparticle relaxation and the electron-boson interactions. Methods of ultrafast optics provide stimulation and selective probing of specific degrees of freedom in solids in order to visualize multidimensional nonequilibrium dynamics on the timescale of lattice vibrations and to reveal dynamics of spontaneously broken symmetries, to elucidate hidden phases and features of light-induced suppression/creation of the superconducting state and to provide new insights into "intertwined" order parameters on ultrashort time scales. Real-time imaging of nonequilibrium dynamics across broad length and time scales can provide important information about the scales over which spin wave functions are coherent. To answer fundamental questions about the size-dependent quantum material dynamics, a novel time- and angle-resolved hemispherical light scattering method is applied. This technique visualizes angular distribution of scattered light at cryogenic temperatures to monitor transient nonequilibrium processes in grains/domains of different size. The fabrication of iron-based superconducting epitaxial films is based on new pulsed laser deposition protocols developed during the project.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.