Spin and orbital dynamics in magneto-resistive manganites measured with femtosecond resonant soft x-ray scattering using FEL pulses

使用 FEL 脉冲通过飞秒共振软 X 射线散射测量磁阻锰氧化物的自旋和轨道动力学

• 批准号: EP/F020112/1
• 负责人: Andrea Cavalleri
• 金额: $ 15.73万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FF020112%2F1
• 关键词: Spin; orbital; dynamics; magneto; resistive

Manganites belong to a family of materials that include high-temperature cuprate superconductors and other complex solids of current interest. These systems are characterized by strongly interacting electrons and by significant electron-lattice coupling, which in turn result in a bewildering variety of interesting phenomena that defy many concepts underpinning our understanding of the solid state. Some of the most interesting phenomena occur when microscopic order is attained, which encompasses periodic arrangements in electronic, magnetic orbital and atomic structures. These ordered states are extremely sensitive to external stimulation, whereby the application of magnetic fields, pressure, electric fields and irradiation with light can switch the system among phases that exhibit colossal changes in their macroscopic behavior. These solids are then not only one of the frontiers of our understanding of the solid state, but may also lead to a variety of new applications in data storage and processing, as well as in novel sensor technologies. In our work, we study the insulator-metal transition triggered by light in the manganites. In the photo-induced insulator-metal transition irradiation with one photon every thousand unit cells results in a cooperative transition of the entire crystal toward a metallic state, with changes in many microscopic parameters at once occurring on the ultrafast timescale. Because this process is very fast, one may be able to exploit it for novel applications in high bit rate data storage and processing. Yet, understanding and optimizing the microscopic phenomena associated with such transition requires that one is able to interrogate the structural parameters of the system with commensurate speed. The timescale of interest is the femtosecond timescale, i.e. that where atoms move and spin patterns rearrange. Our work seeks to extend the same x-ray techniques that have revolutionized modern materials science to the femtosecond timescale. In the research program proposed here, we seek to exploit x-ray free electron lasers to investigate the microscopic dynamics of magneto-resistive manganites. We will use the unprecedented brillance, pulse duration and spatial coherence of Free Electron Laser beams to study the rearrangements of orbital and magnetic superstructures across the ultrafast insulator-metal transition in the manganites. We will exploit femtosecond FEL pulses of coherent 2-nm radiation to perform time-resolved, resonant x-ray scattering experiments, which will yield information on the disordering of orbitals and spins during the transition to the metallic phase. Also, the exploitation of the transverse coherence of these pulses will be used to study the speckle patterns at small angular deviations from the bragg peak, yielding information on static and dynamic rearrangements of the long-range (tens to hundreds of nm) texture. This will be also of great importance because mesoscopic phenomena, nucleation and phase separation are known to subtly underpin the dynamics of these systems.

锰酸盐属于一系列材料，其中包括高温铜酸盐超导体和当前感兴趣的其他复杂固体。这些系统的特点是电子的强烈相互作用和显着的电子-晶格耦合，这反过来又导致了各种令人眼花缭乱的有趣现象，这些现象违背了我们对固态理解的许多概念。当达到微观秩序时，就会发生一些最有趣的现象，其中包括电子、磁轨道和原子结构的周期性排列。这些有序状态对外部刺激极其敏感，因此施加磁场、压力、电场和光照射可以使系统在宏观行为发生巨大变化的阶段之间切换。这些固体不仅是我们理解固态的前沿之一，而且还可能在数据存储和处理以及新型传感器技术方面带来各种新的应用。在我们的工作中，我们研究了亚锰酸盐中光触发的绝缘体-金属转变。在光诱导绝缘体-金属转变中，每千个晶胞用一个光子进行照射，导致整个晶体向金属态协同转变，并且在超快时间尺度上同时发生许多微观参数的变化。由于这一过程非常快，因此人们可以将其用于高比特率数据存储和处理中的新颖应用。然而，理解和优化与这种转变相关的微观现象需要能够以相应的速度询问系统的结构参数。感兴趣的时间尺度是飞秒时间尺度，即原子移动和自旋模式重新排列的时间尺度。我们的工作旨在将彻底改变现代材料科学的 X 射线技术扩展到飞秒时间尺度。在此提出的研究计划中，我们寻求利用 X 射线自由电子激光器来研究磁阻锰酸盐的微观动力学。我们将利用自由电子激光束前所未有的亮度、脉冲持续时间和空间相干性来研究锰酸盐中超快绝缘体-金属转变过程中轨道和磁性超结构的重新排列。我们将利用相干 2 nm 辐射的飞秒 FEL 脉冲来执行时间分辨的共振 X 射线散射实验，这将产生有关在过渡到金属相期间轨道和自旋无序的信息。此外，利用这些脉冲的横向相干性将用于研究与布拉格峰有小角度偏差的散斑图案，从而产生有关长程（数十至数百纳米）纹理的静态和动态重排的信息。这也非常重要，因为已知介观现象、成核和相分离巧妙地支撑了这些系统的动力学。

项目成果

Optical excitation of Josephson plasma solitons in a cuprate superconductor

• DOI: 10.1038/nmat3580
• 发表时间: 2013-06-01
• 期刊: NATURE MATERIALS
• 影响因子: 41.2
• 作者: Dienst, A.;Casandruc, E.;Cavalleri, A.
• 通讯作者: Cavalleri, A.

Bi-directional ultrafast electric-field gating of interlayer charge transport in a cuprate superconductor

• DOI: 10.1038/nphoton.2011.124
• 发表时间: 2011-08-01
• 期刊: NATURE PHOTONICS
• 影响因子: 35
• 作者: Dienst, A.;Hoffmann, M. C.;Cavalleri, A.
• 通讯作者: Cavalleri, A.