Physics of quasicrystals and related alloys

凝聚态物理领域的进步往往需要发现和发展新材料，以扩展或挑战目前的理解。这项拟议的研究既涉及新材料的合成，也涉及对其物理性质的研究。这项提议聚焦于当前感兴趣的一类特定材料，即准晶。除了固体的基本晶体和非晶态结构形式外，1984年还发现了一种被称为准晶的新物质相。该相具有一种新的长程平移有序，称为准周期性，以及一种与经典禁止的对称轴相关的非晶体取向有序。凝聚态物理中的一个中心问题是确定准周期是否导致与晶体和非晶态材料的物理性质显著不同的物理性质。电子在准周期环境中的行为如何？准晶中电子态的性质是什么？准晶中允许什么磁性基态？在准晶发现二十多年后，这些问题仍然受到研究人员的激烈辩论。这项研究通过合成几个准晶和相应的晶体近似物，并用磁化、中子衍射、电阻和磁阻、穆斯堡尔谱和光电子能谱技术研究它们的物理性质，来解决这些悬而未决的问题。这项拟议研究的最终结果将是对准晶的本征磁性、电子输运和电子结构性质有更清晰的理解。十几名研究生/本科生将获得一系列与合成和测量相关的实用技能，以及对各种磁性和电子现象的深入了解。此外，表征良好的准晶的出现将为该领域提供一个新的样品盒，用于研究固体中准周期性的物理效应。

Advances in the field of condensed-matter physics often require the discovery and development of new materials that extend or challenge the current understanding. The proposed research addresses both the synthesis of new materials and the investigation of their physical properties. This proposal focuses on one specific class of materials that are of current interest, namely quasicrystals.In addition to the basic crystalline and amorphous structural forms of solids, a new phase of matter known as quasicrystals was discovered in 1984. This phase has a new type of long-range translational order, called quasiperiodicity, and a non-crystallographic orientational order associated with classically forbidden symmetry axes. A central problem in condensed matter physics is to determine whether quasiperiodicity leads to physical properties which are significantly different from those of crystalline and amorphous materials.How do the electrons behave in a quasiperiodic environment? What is the nature of the electronic states in quasicrystals? What magnetic ground states are allowed in quasicrystals? More than two decades after the discovery of quasicrystals, these questions are still hotly debated by researchers. The proposed research addresses these outstanding questions via the synthesis of several families of quasicrystals and corresponding crystalline approximants and the investigation of their physical properties with the magnetization, neutron diffraction, electrical resisitivity and magnetoresistance, Mossbauer spectroscopy, and photoemission spectroscopy techniques. The end product of the proposed research will be a much clearer understanding of the intrinsic magnetic, electronic transport, and electronic structure properties of quasicrystals. A dozen of graduate/undergraduate students will acquire a range of practical synthesis and measurement related skills as well as in-depth understanding of various magnetic and electronic phenomena. In addition, the availability of well-characterized quasicrystals will provide the field in general with a new toy-box of samples for investigating the physical effects of quasiperiodicity in solids.