Neutron and X-Ray Scattering Studies of Quantum Magnets, With and Without Disorder

在本项目中，我们将对三种材料(a)一维和二维量子磁体，(b) Sr-和过量氧掺杂La2CuO4高温超导体，(c)在微观水平上极度无序的模型晶体绝缘磁体进行全面的实验研究。问题(a)和(b)已经演变成不同的，但密切相关的研究领域。对于铜氧化物，我们对正常和超导态的理解还远远不够。对氧化铜的研究使低维量子磁体的研究复兴，揭示了直到最近才被怀疑的微妙之处。对于无序磁体，出现了与历史依赖性和性质的不可再现性有关的新问题，这需要扩展我们对材料平衡性质的现有理解。这些系统将使用中子和x射线散射技术进行研究。自然界中有各种各样的材料，它们表现出各种各样的特性，如磁性、超导性和半导体电子行为。其中一些材料，如半导体Si或Ga，以及简单的金属，如Al或Cu，现在已经很好地理解了。然而，有许多材料，如陶瓷超导体或磁性合金，人们对它们几乎一无所知。在这个研究项目中，我们的总体策略是利用中子和x射线散射等专门技术在原子水平上观察这些材料，并观察从微观到宏观水平的性质演变。因此，我们的目标是阐明这些材料背后的基本物理学。＊＊＊

9704532 Birgeneau In this project, we will carry out a comprehensive experimental study of three classes of materials (a) one and two-dimensional quantum magnets, (b) Sr- and excess - Oxygen doped La2CuO4 high temperature superconductors, (c) model crystalline insulating magnets which are extremely disordered at the microscopic level. Problems (a) and (b) have evolved into distinct, but closely related areas of research. For the copper oxides our understanding of both the normal and superconducting states is still far from complete. Research in the copper oxides has produced a renaissance in studies of low-dimensional quantum magnets revealing subleties which were barely suspected until the recent past. For the diordered magnets new issues connected with history dependence and irreproducibility of the properties arise which require an extension of our existing understanding of equilibrium properties of materials. These systems will be studied using both neutron and x-ray scattering techniques. %%% There is a remarkable variety of materials in Nature which exhibit properties as varied as magnetism, superconductivity and semiconducting electronic behavior. Some of these materials such as the semiconductors Si or Ga As as well as simple metals such as Al or Cu are by now well understood. There are, however, many materials such as ceramic superconductors or magnetic alloys which are barely understood at all. In this research program, our general strategy is to look at these materials at the atomic level using specialized techniques known as neutron and x-ray scattering and to see how the properties evolve as one goes from the microscopic to the macroscopic level. Our goal is thereby to elucidate the fundamental physics which underlies these materials. ***