Exotic Ground States in New Materials

大多数磁性材料的基态，以及所有被很好理解的磁性材料，其特征在于长程有序和常规元激发的出现，例如自旋波。我们特别感兴趣的是新的磁性材料的家庭，在这种情况下，这是一个无序的低温相可以持续由于存在非常强的自旋波动。这是当前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状态可以在低温下被抑制，它就为一个奇异的基态打开了一个窗口，也许具有质的新的和显着的物理性质。 在磁性材料中，强自旋涨落可以通过三种方式得到鼓励：磁矩可以装饰局部几何形状（通常基于三角形和四面体）在与简单有序状态不相容的固体中-这被称为几何挫折; S=1/2和有效S=1/2磁矩，其支持极端的量子涨落，可以用来装饰晶格;最后，由于由磁平面的堆叠或磁链的聚束构成的三维晶体结构，磁晶格可以有效地是二维或一维的。也就是说，我们可以使用几何挫折，量子涨落或降低维度来增强自旋涨落，从而破坏或削弱磁性材料在低温下显示常规有序的趋势。这项提议旨在探索新的磁性材料，正是这样做。通过进行先进的表征，主要是新的中子和X射线散射技术，我们的目标是阐明在几种这样的材料中随之而来的异国情调的基态的性质，这样的基本原则，他们显示的新现象可以完全理解。 该建议旨在对几个奇异的家庭进行中子散射测量计划。 磁性材料，我们将以原始的单晶形式生长。在过去的六年中，有一个非常戏剧性的文艺复兴的仪器和能力，可用于进行前沿非弹性中子散射。这主要是通过在Sputterus中子源和ISIS开发新的飞行时间中子技术，但也通过NIST，ILL和其他地方的新反应堆技术实现的。最终的结果是，中子散射可以获得的与新材料的静态和动态行为有关的信息的性质与六年前可能获得的信息相比有了质的不同，而且更加全面。该建议旨在将这种新的基础设施和这些新技术应用于与新材料中的奇异磁基态相关的几个热点问题。 该提案主题的一个关键组成部分和起点是一个复杂的材料制备和晶体生长计划，该计划将提供新磁性材料的大而原始的单晶。由此产生的单晶样品将成为这些前沿中子和X射线散射研究的主题。我们处于非常有利的地位，无论是在我们生产感兴趣的单晶的能力方面，还是在与新的中子散射基础设施相关的访问和专业知识方面，都可以在凝聚态物理学的这一非常热门的领域取得真实的进展。

The ground states of most magnetic materials, and all magnetic materials which are well understood, are characterized by the appearance of 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 current 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, perhaps with qualitatively new and remarkable physical properties. 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. That is, we can use geometrical frustration, quantum fluctuations or reduced dimensionality to enhance spin fluctuations and thereby destroy or weaken the tendency for a magnetic material to display conventional order at low temperatures. 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 several such materials, such that the basic 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 pristine and single crystal form. Over the last six years, there has been a very dramatic renaissance in the instrumentation and capabilities available to carry out forefront inelastic neutron scattering. This has occurred mostly through the development of new time-of-flight neutron techniques at the Spallation Neutron Source, and ISIS, but also through new reactor-based techniques at NIST, the ILL, and elsewhere. The net result is that the nature of the information which neutron scattering can access relevant to the static and dynamic behaviour of new materials is qualitatively different and much more comprehensive than what was possible six years ago. This proposal seeks to apply this new infrastructure and these new techniques 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 large and pristine single crystals of the new magnetic materials. The resulting single crystal samples will be the subject of these forefront neutron and x-ray scattering studies. We are exceptionally well positioned, both with respect to our capacity to produce single crystals 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.