Exotic Magnetic Ground States and Ground State Selection in Quantum Materials

大多数磁性材料的基态，以及众所周知的所有磁性材料，都具有长程有序和传统的元素激发的特征，如自旋波。我们对新型磁性材料家族特别感兴趣，但情况并非如此；这就是一种 由于存在非常强的自旋涨落，无序的低温相可以持续存在。这是当代凝聚态研究的一个非常热门的领域，因为人们普遍认为，如果一个传统的有序态在低温下能够被抑制，它就会打开一个窗口，让一个奇异的基态变得明显。适当的量子无序态被认为具有新的和显著的物理性质，例如离域量子自旋激发，这可能为量子计算提供平台。 在磁性材料中，可以通过三种方式鼓励强烈的自旋涨落：磁矩可以修饰与简单有序状态不相容的固体中的局部几何图形(通常基于三角形和四面体)，这被称为几何受挫；可以使S=1/2和有效S=1/2的磁矩来装饰晶格；最后，由于由磁性平面的堆叠或磁链的聚集组成的三维晶体结构，可以使磁性晶格有效地成为二维或一维的。这项提议旨在探索能够做到这一点的新磁性材料。通过进行先进的表征，主要是利用新的中子和X射线散射技术，我们的目标是阐明在这种材料中随之而来的奇异基态的性质，以便能够充分理解它们所显示的新现象背后的原理。 这项提议旨在对我们将以单晶、多晶和外延薄膜形式生长的几种奇异磁性材料进行中子散射测量计划。我们正处于可用于实现前沿非弹性中子的能力的复兴之中 散布。最终的结果是，与六年前相比，新的中子散射仪器提供了性质上不同的、更全面的材料信息。这项提议试图将这一新的基础设施应用于几个与新材料中奇特的磁性基态有关的热门问题。 这项提议主题的一个重要组成部分和起点是一项复杂材料制备和晶体生长计划，该计划将以适当的形式提供新的磁性材料。我们处于非常有利的地位，无论是在我们生产感兴趣的材料的能力方面，还是在获得与新的中子散射基础设施相关的专业知识方面，我们都处于非常有利的地位，能够在这一非常热门的凝聚态物理领域取得真正的进展。

The ground states of most magnetic materials, and all magnetic materials which are well understood, are characterized by long range order and conventional elementary excitations, such as spin waves. We are specifically interested in families of new magnetic materials, where this isn't the case; that is where a disordered low temperature phase can persist due to the presence of very strong spin fluctuations. This is a very topical area of contemporary condensed matter research as it is widely believed that if a conventional ordered state can be suppressed at low temperatures, it opens a window for an exotic ground state to be manifest. Appropriate quantum disordered states are thought to possess qualitatively new and remarkable physical properties, such as delocalized quantum spin excitations, that may provide a platform for quantum computation. Strong spin fluctuations can be encouraged in three ways in magnetic materials: magnetic moments can decorate local geometries (typically based on triangles and tetrahedra) in solids which are incompatible with a simple ordered state this is referred to as geometrical frustration; S=1/2 and effective S=1/2 magnetic moments, which support extreme quantum fluctuations, can be made to decorate the lattice; and finally the magnetic lattice can be effectively two or one dimensional due to a three dimensional crystal structure which is made of a stacking of magnetic planes, or a bunching together of magnetic chains. This proposal seeks to explore new magnetic materials which do precisely this. By carrying out advanced characterization, primarily with new neutron and x-ray scattering techniques we aim to elucidate the nature of the exotic ground states which ensue in such materials, such that the principles that underlie the novel phenomena they display can be fully understood. This proposal seeks to carry out programs of neutron scattering measurements on several families of exotic magnetic materials that we will grow in single crystalline, polycrystalline and epitaxial thin film form. We are in the midst of a renaissance in the capabilities available to carry out forefront inelastic neutron scattering. The net result is that new neutron scattering instrumentation provides qualitatively different, and much more comprehensive, information on materials than was possible six years ago. This proposal seeks to apply this new infrastructure to several topical problems related to exotic magnetic ground states in new materials. A crucial component and starting point for the themes of this proposal is a program of sophisticated materials preparation and crystal growth which will provide new magnetic materials in appropriate forms. We are exceptionally well positioned, both with respect to our capacity to produce materials of interest, and with respect to access and expertise associated with the new neutron scattering infrastructure, to make real progress in this very topical area of condensed matter physics.