Neutron and X-Ray Scattering Studies of Low Dimensional Quantum Magnets

这个实验凝聚态物理项目采用中子和x射线散射技术来研究三种材料：(a)锶和过量氧掺杂的La2CuO4高温超导体(b) 1D和2D量子磁体(c)无序和/或竞争相互作用的模型材料。La2-xSrxCuO4和La2CuO4+y的研究将集中在不匹配的磁性和电荷有序以及伴随的低能自旋动力学上，特别是在欠掺杂的情况下。数据将在所谓的条纹图中进行分析。研究领域(b)和(c)在稀释自旋-佩尔斯材料Cu1-xMgxGeO3中完美地结合在一起，其中磁性和结构超晶格顺序相互竞争。该系统将使用中子和同步加速器x射线散射技术作为x的函数进行研究。实验将在零场和高场进行，其中结构顺序分别为相称和不相称。将探讨二维材料Sr2Cu3O4Cl2中的“有序自无序”现象，包括掺杂诱导的无序所预期的新效应。最后，量子蒙特卡罗技术将用于一维和二维量子自旋系统的建模。所研究的材料有许多实际应用，从超导电子设备到磁记录器的读取头。在这个项目中接受教育的学生将在我们的大型国家设施中发挥领导作用。这个研究项目研究属于“高度相关电子材料”技术范畴的材料的微观物理学，最著名的例子是高温超导体。这种材料最重要的微观特征是，材料中任何电子的行为方式在细节上取决于它周围的电子在做什么。事实证明，这是一个令人惊讶的困难问题，具有根本利益，但具有许多实际后果。这里的一般策略是从原子水平开始，看看随着长度尺度从微观到宏观逐渐增加，性质是如何演变的。作为一个具体的例子，La2CuO4等材料作为掺杂的函数，从二维磁体到高温超导体再到普通金属，不断演变。研究目标是了解这种演变的本质，重点是处于不同状态之间过渡区域的材料。由于这项工作和其他人的相关工作，我们希望对氧化铜超导材料中的各种相及其转变有一个完整的了解。这将反过来使社区能够设计更好的材料和创造新的设备。事实上，基于高度相关电子材料的设备已经出现在市场上。参与该项目的学生通常会在研究型大学、国家实验室、以技术为基础的行业和管理咨询领域从事职业，从而为美国的科学和经济做出重大贡献。

This experimental condensed matter physics project employs neutron and x-ray scattering techniques to investigate three classes of materials: (a) Sr-and excess Oxygen doped La2CuO4 high temperature superconductors (b) 1D and 2D quantum magnets (c) model materials with disorder and/or competing interactions. The research in La2-xSrxCuO4 and La2CuO4+y will focus on the incommensurate magnetic and charge ordering and the concomitant low energy spin dynamics, most especially in the under-doped regime. The data will be analyzed in the so-called stripe picture. Research areas (b) and (c) come together beautifully in the diluted spin-Peierls material Cu1-xMgxGeO3 where magnetic and structural superlattice order compete. This system will be studied as a function of x using both neutron and synchrotron x-ray scattering techniques. Experiments will be carried out both at zero field and at high fields where the structural order is respectively commensurate and incommensurate. The "order from disorder" phenomenon in the 2D material Sr2Cu3O4Cl2, including the novel effects expected from doping-induced disorder, will be explored. Finally, quantum Monte Carlo techniques will be used to model the 1D and 2D quantum spin systems. The materials studied have many practical applications varying from superconducting electronic devices to read heads in magnetic recorders. The students educated in this program will play a leadership role at our large national facilities. %%%This research program investigates the microscopic physics of materials that fall in the technical category of "highly correlated electronic materials" The best known examples are high temperature superconductors. The most important microscopic signature of such materials is that the way any electron in the material behaves depends in detail on what the electrons surrounding it are doing. This turns out to be a surprisingly difficult problem of fundamental interest but with many practical ramifications. The general strategy here is to begin at the atomic level and to look at how the properties evolve as the length scale is increased progressively from the microscopic to the macroscopic. As a specific example, materials such as La2CuO4 as a function of doping evolve continuously from two dimensional magnets to high temperature superconductors to normal metals. The research goal is to understand the nature of this evolution with emphasis on materials which are in the transition region between different states. As a result of this and related work by others we hope to arrive at a complete understanding of the various phases and their transitions in copper oxide superconducting materials. This will in turn enable the community to design better materials and to create new devices. Indeed, devices based on highly correlated electronic materials are already appearing in the marketplace. Students involved in this project typically pursue careers at research universities, national laboratories, technology-based industries and in management consulting and thereby contribute significantly to both U.S. science and the economy.