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类材料：（a）Sr和过量氧掺杂的La 2CuO 4高温超导体（B）一维和二维量子磁体（c）具有无序和/或竞争相互作用的模型材料。在La 2-xSrxCuO 4和La 2CuO 4 +y的研究将集中在无公度的磁性和电荷有序和伴随的低能自旋动力学，特别是在欠掺杂制度。数据将在所谓的条纹图中进行分析。研究领域（B）和（c）在稀释的自旋Peierls材料Cu 1-xMgxGeO 3中完美地结合在一起，其中磁性和结构超晶格有序竞争。 这个系统将被研究作为一个功能的x使用中子和同步辐射X射线散射技术。 实验将在零场和高场进行，其中结构顺序分别是公度和不公度的。将探讨二维材料Sr 2Cu 3 O 4Cl 2中的“无序有序”现象，包括掺杂诱导的无序预期的新效应。最后，量子蒙特卡罗技术将被用来模拟1D和2D量子自旋系统。 所研究的材料具有许多实际应用，从超导电子器件到磁记录器中的读取头。在这个计划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。该研究计划研究属于“高度相关电子材料”技术类别的材料的微观物理学，最着名的例子是高温超导体。这类材料最重要的微观特征是，材料中任何电子的行为都详细取决于周围电子的行为。事实证明，这是一个令人惊讶的困难问题，涉及根本利益，但有许多实际后果。这里的一般策略是从原子水平开始，并观察随着长度尺度从微观到宏观逐渐增加，性质如何演变。作为一个具体的例子，诸如La 2CuO 4的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连续地演变。研究目标是了解这种演变的性质，重点是处于不同状态之间过渡区的材料。 由于这项工作和其他人的相关工作，我们希望能够完全理解氧化铜超导材料中的各个相及其转变。这将反过来使社区能够设计更好的材料并创造新的设备。事实上，基于高度相关的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在研究型大学、国家实验室、技术型行业和管理咨询领域从事职业，从而为美国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.