Spin behavior in magnetic and superconducting oxides

非技术摘要：当电子孤立时，电子的自旋是一种简单的量子力学性质，但当电子自旋在固体中相互作用时，可以观察到许多奇妙的现象。磁性和超导电性是自旋发挥开创性作用的两个主要例子。PI和他的团队基于在样品上扫描纳米级传感器的想法开发了显微镜，以便探测电荷和自旋性质，并将其细化到原子尺度。他们使用这些技术来研究具有不同寻常的磁性和电学性质的新锰氧化物，以及可以在电荷和自旋分布中产生规则图案的超导铜氧化物。这些研究对于理解自旋在复杂的磁性氧化物和超导氧化物中的作用具有重要意义，这将有助于改进现有的材料，并有助于设计新的材料用于未来的应用。技术摘要：在本方案中，重点介绍了将用新型低温自旋极化扫描隧道显微镜(SP-STM)对感兴趣的氧化物进行的实验。尽管对高温超导体相图的理解已经取得了很大的进展，但在超导相的性质、其他相的存在和性质以及所有这些有序参数在微观水平上是竞争还是共存等问题上仍然存在根本的问题。所有这些问题在相图的伪隙区域尤为重要，这个区域延伸到比超导更低的掺杂和更高的温度，也是激烈辩论的话题。电荷密度波和自旋密度波(CDW，SDW)已被报道存在于该区域，但到目前为止，大多数测量都是使用提供平均性质的体探针进行的。SP-STM特别适合于提供原子尺度的微观信息。其他扫描探头也被用来提高我们对这些材料和现象的理解。这两个新的氧化物具有327晶体结构：一个是超导铜酸盐[(LaSrCa)3Cu2O6+d]，另一个是磁性锰氧化物[La2-2xSr1+2xMn2O7]。之所以选择这些材料，是因为它们的结构促进了优异的切割特性，这对于STM研究产生干净、有序的表面是必不可少的，还因为它们允许研究反铁磁相互作用和CDW/SDW在铜酸盐中的作用以及锰氧化物中的电荷、自旋和轨道有序性等基本问题。

Non-technical Abstract:The spin of an electron is a simple quantum mechanical property when the electron is isolated, but when electron spins interact inside a solid a large variety of wonderful phenomena can be observed. Magnetism and superconductivity are two major examples where spins play a seminal role. The PI and his team have developed microscopes based on the idea of scanning a nanoscale sensor over the sample in order to probe the charge and spin properties down to the atomic scale. They use these techniques to study new manganese oxides that have unusual magnetic and electrical properties, and superconducting copper oxides that can produce regular patterns in their charge and spin distributions. These studies are important in order to understand the role of spin in complex magnetic and superconducting oxides, which will serve to improve current materials and will help in the design of new materials for future applications.Technical Abstract:In this proposal, experiments to be performed on interesting oxides with a new low temperature spin polarized scanning tunneling microscope (SP-STM) are highlighted. While there has been much progress in the understanding of the phase diagram for high temperature superconductors, there are still fundamental questions about the nature of the superconducting phase, the presence and properties of other phases, and whether all these order parameters compete or coexist at the microscopic level. All these issues are particularly important in the pseudogap region of the phase diagram, an area that extends to lower doping and higher temperatures than superconductivity, and the topic of intense debate. Charge and spin density waves (CDW, SDW) have been reported to exist in this region, but so far most measurements are done with bulk probes that provide average properties. The SP-STM is particularly well suited to provide microscopic information down to the atomic scale. Other scanning probes are also used to improve our understanding of these materials and phenomena. This proposal focuses on two newer oxides with the 327 crystal structure: one is a superconducting cuprate [(LaSrCa)3Cu2O6+d] and the other a magnetic manganite [La2-2xSr1+2xMn2O7]. These materials were chosen because their structure promotes excellent cleaving characteristics that are essential to produce a clean, ordered surface for STM studies, and because they allow the study of fundamental questions on the role of antiferromagnetic interactions and CDW/SDW in the cuprates, and charge, spin, and orbital ordering in the manganites.