Investigation of optically-driven supercondcutors using pump-probe Raman scattering

非技术摘要超导电性的特征是完全失去电阻。它是一种量子状态，由电子电荷和轨道、磁性和原子振动的强烈相互作用而产生。许多材料中的具体机制让科学家们感到困惑。这个项目利用最近发展起来的一种实验技术，泵浦-探测拉曼光谱，来研究所谓的暂态超导电性。这些都发生在非常短的激光脉冲击中材料后，将一些电子踢出它们的轨道，或者诱导原子的大幅振动。材料可以短暂地进入不同的瞬变状态，例如，超导体将失去超导电性，也可能发生相反的情况--在正常情况下不表现出超导电性的材料可能会出现超导电性。时间分辨的拉曼散射创建了一部电影，展示了这些状态是如何发展的，以及它们是如何回到原始状态的。这个项目背后的主要想法是制作这样的超导体电影，以揭示原本隐藏的量子过程。这些知识被用来检验关于超导机制的想法，并有助于将超导体用于实际应用。这项工作是在科罗拉多大学博尔德分校的超快激光光谱学实验室进行的，该实验室是用早些时候由国家科学基金会提供的资金建造的。该项目对研究生和本科生的教育和培训做出了贡献。技术摘要该项目专注于超导体在吸收超短激光脉冲后不久的开创性测量。其目的是从实验上研究铜氧化物平衡超导电性的神秘机制，以及光致非平衡超导电性的一般现象。在实验中，被研究的样品在短激光脉冲的驱动下失去平衡，另一个延时脉冲的拉曼散射将探测其弛豫。这些实验跟踪声子、电子温度和超导带隙在系统热化时的时间演化。这一新的方法阐明了最近报道的插层C60和一些铜氧化物中的光驱动超导中的能量流动、瞬时时间尺度和加热。对解释这一现象的非线性声子学和约瑟夫森电流机制进行了验证。这一领域的进展最终将为开发涉及超导光学控制的新材料和新器件奠定基础。这项工作是在科罗拉多大学博尔德分校的超快激光光谱学实验室进行的，该实验室是用之前由国家科学基金会提供的资金建造的。该项目有助于研究生和本科生的教育和培训。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 Superconductivity is characterized by a complete loss of electrical resistance. It is a quantum state that arises out of strong interactions of electronic charges and orbitals, magnetism, and vibrations of atoms. The specific mechanisms in many materials are puzzling to scientists. This project takes advantage of a recently developed experimental technique, pump-probe Raman spectroscopy, to investigate superconductivity in so-called transient states. These occur right after a very short laser pulse hits the material and either kicks some electrons out of their orbits or induces large amplitude vibrations of the atoms. The material can briefly go into a different transient state, e.g., a superconductor will lose superconductivity, or the opposite can happen – superconductivity may arise in a material that does not exhibit it under normal circumstances. Time-resolved Raman scattering creates a movie of how these states develop and how they come back to the original state. The main idea behind this project is to make such movies of superconductors to reveal otherwise hidden quantum processes. This knowledge is used to test ideas about mechanisms of superconductivity and helps to harness superconductors for practical applications. The work is carried out at the ultrafast laser spectroscopy laboratory at the University of Colorado-Boulder built with the funds provided earlier by the National Science Foundation. The project contributes to the education and training of graduate and undergraduate students.Technical AbstractThis project focuses on groundbreaking measurements of superconductors shortly after absorption of an ultrashort laser pulse. The purpose is to experimentally investigate still enigmatic mechanisms of equilibrium superconductivity in copper oxides as well as the general phenomenon of light-induced nonequilibrium superconductivity. In the experiments, the investigated sample is driven out of equilibrium by a short laser pulse, and Raman scattering from another time-delayed pulse will probe its relaxation. These experiments track time-evolution of phonons, electronic temperature, and the superconducting gap as the system thermalizes. This novel approach elucidates energy flows, transient timescales, and heating in optically-driven superconductivity recently reported in intercalated C60 and some copper oxides. Nonlinear phononics and Josephson current-based mechanisms suggested as explanations of this phenomenon are tested. Advances in this area will ultimately underlie development of new materials and devices involving optical control of superconductivity. The work is carried out at the ultrafast laser spectroscopy laboratory at the University of Colorado-Boulder built with the funds provided previously by National Science Foundation. The project contributes to the education and training of graduate and undergraduate students.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.