Correlated Electron Effects in Small Clusters in Low Temperatures Molecular Beams

*****非技术摘要****由几个到几百个原子组成的金属团簇是典型的纳米级物体。在不受支撑结构影响的真空分子束中研究了它们的内在性质。当金属中传导电子的运动相互关联时，会产生许多有趣的性质。其中最著名的是铁磁性和超导性。这个项目将使用分子束研究来追踪这些特性的演变，作为簇大小的函数。例如，由5个原子组成的铁团簇的磁性与由500个原子组成的铁团簇的磁性不同，两者都表现出可识别的整体磁性特征。深入了解磁性的这些进化趋势将有助于设计新型纳米磁性材料，这对唱片业非常重要。参与这项研究的学生将学习科学概念和最先进的技术，这将为他们在学术、工业或政府研究领域的职业生涯做好准备。此外，还计划向高中科学教师推广。本项目由材料研究部的凝聚态物理项目和物理部的原子、分子和光学物理项目支持。*****技术摘要****该个人研究者奖支持一个项目，该项目使用GIT开发的最先进的低温分子束方法来测量各种金属簇的性质，作为质量和温度的函数（T=10-300 K）。在非常低的温度下，无支撑的团簇尤为重要，这不仅是因为它们的性质可以通过精确的尺寸知识来精确测量，而且还因为光束中相对较大一部分的团簇在量子力学基态中被冻结。这种几乎未被探索的物质状态为研究涉及铁磁性、铁电性和超导性的电子性质和电子相变提供了一个独特的机会。铁电相变与Nb， V和Ta簇中的超导性的关系将被研究。此外，还将对团簇铁磁性进行研究。特别是对于钴簇，已经观察到每个原子具有2个玻尔磁子的基态和每个原子具有约1个玻尔磁子的电子激发态。这一发现提示了分子磁性向体流动铁磁性演化的一种机制。参与这项研究的学生将学习科学概念和最先进的技术，这将为他们在学术、工业或政府研究领域的职业生涯做好准备。此外，还计划向高中科学教师推广。本项目由材料研究部的凝聚态物理项目和物理部的原子、分子和光学物理项目支持

*****NON-TECHNICAL ABSTRACT**** Metal clusters, composed of a few to a few hundred atoms, are prototypical nanoscale objects. Their intrinsic properties are studied in molecular beams in a vacuum where they are not affected by supporting structures. Many interesting properties result when the motion of the conduction electrons in metals becomes correlated. The best known of these are ferromagnetism and superconductivity. This project will use molecular beam studies to trace the evolution of these properties as a function of cluster size. For example, the magnetic properties of an iron cluster composed of 5 atoms are different than those of a cluster with 500 atoms, and both exhibit recognizable bulk magnetic features. Insight into these evolutionary trends in magnetism will help in designing novel nano-magnetic materials, which are important for the recording industry. The students participating in this research will learn scientific concepts and state-of-the-art techniques, which will prepare them for careers in academic, industrial, or governmental research. In addition, outreach to high school science teachers is planned. This project is supported by the Condensed Matter Physics program in the Division of Materials Research and the Atomic, Molecular, and Optical Physics program in the Physics Division.*****TECHNICAL ABSTRACT**** This individual investigator award supports a project using state of the art low-temperature molecular beam methods developed at GIT to measure properties of a wide variety of metal clusters as a function of mass and temperature (T=10-300 K). Support-free clusters at very low temperatures are particularly important, not only because their properties can be accurately measured with precise knowledge of their size, but also because a relatively large fraction of the clusters in the beam are frozen in their quantum mechanical ground states. This virtually unexplored state of matter provides a unique opportunity to investigate electronic properties and electronic phase transitions involving ferromagnetism, ferroelectricity and superconductivity. The relationship of the ferroelectric phase transition to superconductivity in Nb, V, and Ta, clusters will be examined. In addition cluster ferromagnetism will be investigated. In particular for cobalt clusters a ground state with 2 Bohr magnetons per atom and an electronically excited state with about 1 Bohr magneton per atom has been observed. This observation suggests a mechanism for the evolution of molecular magnetism to bulk itinerant ferromagnetism. The students involved with this research will learn scientific concepts and state-of-the-art techniques, which will prepare them for careers in academic, industrial, or governmental research. In addition, outreach to high school science teachers is planned. This project is supported by the Condensed Matter Physics program in the Division of Materials Research and the Atomic, Molecular, and Optical Physics program in the Physics Division