Polaron-Induced Local Distortions in Correlated Electron Systems

相关电子系统中极化子引起的局部畸变

• 批准号: 9705117
• 负责人: Frank Bridges
• 金额: $ 24.5万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-09-15 至 2001-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9705117&HistoricalAwards=false
• 关键词: Polaron; Induced; Local; Distortions; Correlated

9705117 Bridges This is a new project which proposes X-Ray absorption fine structure (XAFS) measurements on systems exhibiting metal- insulator transitions and Colossal Magnetoresistance (CMR) effects, such as La1-xCaxMnO3. In these oxides, the large magnetoresistance near the ferromagnetic transition temperature, Tc, is now attributed to a novel coupling between magnetism, the electron system and local lattice distortions and, in a recent paper, we have shown that the transition from metallic to insulating behavior correlates well with a rapid increase in the amplitude of the local distortions which are believed to be polaronic in origin. However, the nature, symmetry and extent of the atomic displacements are not yet known and are needed for modeling these unusual transport effects. XAFS measurements as a function of temperature and magnetic field will enable us to probe the details of the local structural distortions about the metal atoms and provide this crucial information. %%% This is a new project which proposes X-Ray absorption fine structure (XAFS) measurements on systems such as La1-xCaxMnO3 which exhibit novel features in their magnetic and electrical behavior that appear to be related to the atomic structure of the material. Recent theoretical models suggest that the arrangement of the atoms become distorted at the same temperature at which the magnetic properties disappear and it is suggested that these distortions contribute to the large observed increase in the resistance to the flow of electrical current. Our initial study supports such a model, but details about the arrangements of the atoms are not yet known. We will use x-ray absorption techniques to investigate the distortions about a given atom at various temperatures and magnetic fields. We need to determine which atoms are distorted and the range and magnitude of the distortions to test and improve the models of this unusual behavior. This novel connection between the microscopic atomic arrangement and the electrical properties involves new physics and may lead to new applications since such materials are potentially useful to make devices for reading and writing information on computer disk. ***

9705117电桥这是一个新项目，它建议对表现出金属-绝缘体转变和巨磁电阻效应的系统进行X射线吸收精细结构(XAFS)测量，例如La_(1-x)CaxMnO_3。在这些氧化物中，铁磁转变温度附近的大磁阻现在被归因于磁性、电子系统和局域晶格扭曲之间的一种新的耦合，并且在最近的一篇论文中，我们已经证明了从金属行为到绝缘行为的转变与局域扭曲幅度的迅速增加密切相关，人们认为局域失真的起源是极化子。然而，原子位移的性质、对称性和程度尚不清楚，需要用来模拟这些不寻常的输运效应。作为温度和磁场函数的XAFS测量将使我们能够探索关于金属原子的局部结构扭曲的细节，并提供这一关键信息。%这是一个新项目，它建议对La1-xCaxMnO3等系统进行X射线吸收精细结构(XAFS)测量，这些系统在其磁和电行为上显示出新的特征，似乎与材料的原子结构有关。最近的理论模型表明，在相同的温度下，原子的排列发生了扭曲，在这个温度下，磁性质消失了，并提出了这些扭曲导致了观察到的电流流动阻力的大幅增加。我们最初的研究支持这样一个模型，但关于原子排列的细节尚不清楚。我们将使用x射线吸收技术来研究给定原子在不同温度和磁场下的扭曲。我们需要确定哪些原子是扭曲的，以及扭曲的范围和程度，以测试和改进这种不寻常行为的模型。微观原子排列和电学性质之间的这种新颖的连接涉及新的物理并且可能导致新的应用，因为这种材料潜在地可用于制造用于在计算机盘上读取和写入信息的设备。***