Renormalized Insulators: On the Verge of Magnetism

*技术摘要*这个项目旨在将强关联电子系统的知识扩展到强相互作用或高度重整化的绝缘体处于磁性边缘的区域。PI及其合作者之前的研究表明，由于半导体物理和磁学的重要性，这是一个非常丰富的研究脉络。这些被化学取代的小带隙绝缘体中固有的竞争相互作用经常导致在存在强关联和无序的情况下的量子相变。将要研究的典型系统包括铁基非磁性绝缘体，如FeSi、FeS2和相关材料，在这些材料中，可以通过掺杂实现从强关联绝缘体到磁性金属的转变。我们的目标是发现当载流子被掺杂到这些强关联绝缘体中时，存在哪些新的现象，将它们置于低载流子密度、无序、磁性以及在某些情况下，有限尺寸都是重要方面的独特区域。此外，我们还将探索最近在具有FeSi晶体结构的单硅化物和锗化物材料的薄膜中发现的磁性Skyrmion相的成核、成像和控制。许多层次的学生以及高中教师将探索这些材料，寻找可能在未来技术中利用的新的运输、磁性、热力学和光学性质。*非技术摘要*为了加速使我们几乎可以在地球上任何地方进行高速计算和信息存储的技术革命，新的想法是必不可少的。半导体器件设计的一个进步途径，称为自旋电子学，寻求利用磁性自由度，其程度与当今硅技术中使用的电荷自由度相同。随着科学家试图控制或操纵电子的自旋，也就是电子的固有磁性，他们认识到了磁性和半导体材料的用途。这项工作试图通过研究一系列由过渡金属和硅或锗组成的化合物来扩展我们对磁性半导体的知识，在这些化合物中，半导体和磁性行为都已知出现。这些系统提供的化学灵活性，同时保持共同的晶体结构，允许对它们的物理性质进行巨大的控制，使它们成为在半导体物理和磁性的交叉点发现新行为的理想选择。此外，这些化合物中的一个家族的基本晶体结构的不同寻常的对称性已经被证明在一定的温度和磁场范围内诱导出约100 nm大小的环状磁性结构，即所谓的磁天平。这个项目调查了成核、成像和控制这些新型磁结构的必要元素，作为一项基础性的探索，并评估它们与未来技术的可能相关性。许多层次的学生以及高中教师将探索这些磁性半导体的晶体、薄膜和纳米线形式的磁性、电学、光学和热力学性质。

****Technical Abstract****This project is designed to extend knowledge of strongly correlated electron systems into the regime of strongly interacting, or highly renormalized, insulators on the verge of magnetism. Previous investigations by the PI and collaborators have indicated that this is a very rich vein of research because of the importance of both semiconductor physics and magnetism. The competing interactions inherent in these carefully characterized chemically substituted small band-gap insulators often lead to quantum phase transitions in the presence of strong correlations and disorder. Typical systems that will be investigated include iron-based non-magnetic insulators, such as FeSi, FeS2, and related materials, where a transition from a strongly correlated-insulator-to-magnetic metal transition can be accessed by doping. The goals are to discover what novel phenomena exist when carriers are doped into these strongly correlated insulators placing them in the unique regime where low carrier density, disorder, magnetism, and, in some cases, finite size are all important aspects. In addition we will be exploring the nucleation, imaging, and control of the magnetic Skyrmion phases that have recently been discovered in the mono-silicide and -germanide materials having the FeSi crystal structure in thin films of these materials. Students on many levels, as well as high school teachers will explore these materials searching for novel transport, magnetic, thermodynamic, and optical properties that may be exploited in future technologies.****Non-Technical Abstract****In order to accelerate the technological revolution that has placed high speed computation and information storage at our fingertips almost anywhere on Earth, new ideas are essential. One pathway for progress in semiconductor device design, known as spintronics, seeks to make use of the magnetic degrees of freedom to the same extent that charge degrees of freedom are used in present day silicon technologies. As scientists have sought to control or manipulate the electron spin, the intrinsic magnetic property of electrons, they have recognized the utility of materials that are both magnetic and semiconducting. This work seeks to extend our knowledge of magnetic semiconductors by investigating a series of compounds composed of transition metals and silicon or germanium where both semiconducting and magnetic behavior are known to emerge. The chemical flexibility that these systems offer while maintaining a common crystal structure allows enormous control over their physical properties making them ideal for discovering new behaviors at the intersection of semiconductor physics and magnetism. Also, the unusual symmetry of the underlying crystal structure of one family of these compounds has been shown to induce ~100 nm sized toroidal shaped magnetic structures, known as magnetic Skyrmions, for a range of temperatures and magnetic fields. This project investigates the necessary elements for nucleating, imaging, and controlling these novel magnetic structures both as a fundamental exploration and to assess their possible relevance for future technologies. Students on many levels, as well as high school teachers, will be exploring magnetic, electric, optical, and thermodynamic properties of these magnetic semiconductors in crystalline, thin film, and nanowire form.