Physics of quasicrystals and related alloys

凝聚态物理领域的进步往往需要发现和开发新材料，以扩展或挑战当前的理解。提出的研究既涉及新材料的合成，也涉及其物理性质的研究。这一建议侧重于当前感兴趣的一类特定材料，即准晶体。除了固体的基本晶体和非晶结构形式外，1984年还发现了一种被称为准晶体的新物质相。该相具有一种新型的长程平动顺序，称为准周期性，以及与经典禁止的对称轴相关的非晶体取向顺序。凝聚态物理的一个中心问题是确定准周期性是否会导致与晶体和非晶态材料明显不同的物理性质。电子在准周期环境中的行为是怎样的？准晶体中电子态的本质是什么？准晶体中允许存在什么样的磁性基态？在发现准晶体20多年后，这些问题仍在研究人员之间激烈争论。本研究通过合成几个家族的准晶体和相应的晶体近似物，并利用磁化、中子衍射、电阻率和磁阻、穆斯堡尔光谱和光发射光谱技术研究它们的物理性质，解决了这些悬而未决的问题。所提出的研究的最终结果将是对准晶体的固有磁性、电子输运和电子结构性质有更清晰的了解。十几名研究生/本科生将获得一系列实用的合成和测量相关技能，以及对各种磁和电子现象的深入了解。此外，充分表征准晶体的可用性将为研究固体准周期性的物理效应提供一个新的样品盒。

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.