Spin behavior in magnetic and superconducting oxides

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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.