Femtosecond Studies of Coupled Electron-Lattice Dynamics in Doped Perovskite Manganites

这个凝聚态物理项目旨在阐明掺杂钙钛矿锰氧化物中金属-绝缘体相变附近的电子-晶格耦合、软模动力学和自旋反转过程。飞秒时间分辨光学响应技术将被用来测量各种过程的动力学，这些过程决定了锰氧化物的不寻常的传输特性。主要目的是研究电荷载流子及其周围晶格形变的耦合动力学。用时域法研究这些强阻尼响应的优势是显而易见的，特别是在结构相变附近，软模式具有明显的强阻尼或过阻尼的特点。磁弹性耦合对理解锰氧化物的低温自旋动力学具有重要意义。有关自旋动力学的信息将被用来测试对这个参数敏感的各种理论方法。飞秒可调谐激光系统将用于脉冲受激拉曼散射(ISRS)、泵浦探测瞬时反射率和磁光克尔效应的实验。通过ISRS测量系统地研究软光学声子模的固有频率和衰减，将提供关于这些强关联电子系统的电子和结构不稳定性以及相变的新信息。我们的磁场依赖研究的目的是阐明移动载流子的关联效应以及它们对掺杂锰氧化物磁结构的依赖关系。参与该项目的学生将接受包括现代光学、材料科学和计算建模在内的跨学科领域的培训。由于在室温下观察到的巨大磁阻效应，人们对作为磁性传感器和探测器的特殊候选材料的锰氧化物重新燃起了兴趣。薄膜为各种技术领域的应用开辟了新的可能性，例如磁随机存取存储器和硬盘驱动器的读头。这个研究项目的目的是通过研究电荷载流子和周围晶格变形的耦合动力学来阐明掺杂锰氧化物的异常磁输运性质。飞秒时间分辨光学响应技术将被用来测量各种过程的动力学，这些过程决定了锰氧化物的不寻常的传输特性。磁场相关研究的目的是揭示移动载流子的关联效应及其对掺杂锰氧化物磁结构的依赖关系。自旋动力学的实验研究可以用来检验对这个参数敏感的各种理论方法。这些基础研究将提供关于在这个强关联的物质系统中控制大的自旋相关输运的机制的新信息。研究生和本科生在这个项目工作期间将接受的培训将为他们在工业、学术或政府部门从事有吸引力的材料科学或光学相关职业做好准备。

This condensed matter physics project seeks to elucidate electron-lattice coupling, soft mode dynamics, and spin-flip processes near the metal-insulator phase transition in doped perovskite manganites. Femtosecond time-resolved optical response techniques will be employed to measure the dynamics of the various processes that dictate the unusual transport properties of the manganese oxides. The primary objective is to study the coupled dynamics of the charge carriers and that of the lattice deformations, which surround them. The advantages of the time-domain approach to investigate these heavily damped responses are clear, especially near structural phase changes where the soft modes are characteristically heavily damped or over damped. Magneto-elastic coupling is important to understand the low-temperature spin dynamics of manganite. Information about the spin dynamics will be used to test various theoretical approaches that sensitive to this parameter. A femtosecond-tunable laser system will be employed for impulsive-stimulated Raman scattering (ISRS), pump-probe transient reflectivity and magneto-optical Kerr-effect experiments. Systematic studies of the natural frequency and damping of the soft optical phonon modes by ISRS measurements will provide new information about electronic and structural instabilities and phase changes of these strongly correlated electron systems. The goal of our magnetic field-dependent studies is to elucidate correlation effects of the mobile charge carriers and their dependence on the magnetic structure of the doped manganese oxides. The students involved in this project will be trained in an interdisciplinary field including modern optics, material science, and computational modeling.Interest in the manganese oxides as exceptional candidates for magnetic sensors and detectors has been rekindled because of the colossal magnetoresistance effect observed in these materials at room temperature. Thin films open up new possibilities for applications in diverse areas of technology such as magnetic random access memories and read heads for hard disk drives. The goal of this research program is to elucidate the unusual magneto-transport properties of doped manganese oxides by studying the coupled dynamics of the charge carriers and that of the lattice deformations that surround them. Femtosecond time-resolved optical response techniques will be employed to measure the dynamics of the various processes that dictate the unusual transport properties of the manganese oxides. The goal of the magnetic field-dependent studies is to reveal correlation effects of the mobile charge carriers and their dependence on the magnetic structure of the doped manganese oxides. Experimental studies of the spin dynamics can be used to test various theoretical approaches that are sensitive to this parameter. These fundamental studies will provide new information about the mechanism that governs the large spin-dependent transport in this strongly correlated material system. The training that graduate and undergraduate students will receive while working on this project will prepare them for attractive material science or optics related careers in industry, academe, or government.