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

这个凝聚态物理学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，软模动力学和自旋翻转过程。 飞秒时间分辨的光学响应技术将被用来测量的各种过程，决定不寻常的锰氧化物的传输特性的动态。 其主要目的是研究耦合动力学的电荷载流子和晶格变形，围绕他们。 时域方法研究这些重阻尼响应的优点是显而易见的，特别是在结构相变附近，其中软模式的特征是重阻尼或过阻尼。 磁弹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-探测瞬态反射率和磁光克尔效应实验。系统研究软光学声子模的固有频率和阻尼的ISRS测量将提供新的信息，这些强关联电子系统的电子和结构的不稳定性和相变。 我们的磁场依赖性研究的目标是阐明相关效应的移动的电荷载流子和它们的依赖于掺杂锰氧化物的磁结构。参与该项目的学生将接受现代光学、材料科学和计算建模等跨学科领域的培训。由于在这些材料中观察到的室温下的巨磁阻效应，人们对锰氧化物作为磁传感器和探测器的特殊候选者的兴趣重新燃起。薄膜为各种技术领域的应用开辟了新的可能性，例如磁性随机存取存储器和硬盘驱动器的读取头。这项研究计划的目标是通过研究电荷载流子的耦合动力学和围绕它们的晶格变形来阐明掺杂锰氧化物的不寻常的磁输运性质。 飞秒时间分辨的光学响应技术将被用来测量的各种过程，决定不寻常的锰氧化物的传输特性的动态。 磁场依赖性研究的目的是揭示移动的电荷载流子的相关效应及其对掺杂锰氧化物磁结构的依赖性。 自旋动力学的实验研究可以用来测试对这个参数敏感的各种理论方法。 这些基础研究将提供新的信息，在这个强相关的材料系统的机制，管理大自旋相关的运输。 研究生和本科生在从事该项目时将接受的培训将为他们在工业，工业或政府中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.