Competing Ground States and Disorder in Correlated Electron Systems

该项目涉及应用固态磁共振技术来解决当前与选定相关电子系统中竞争基态相关的问题。该方法是基于对几种材料的检查，其中反铁磁性与顺磁性费米液相（可能还有超导性）或自旋-佩尔斯相竞争。正在研究的材料来自两个家族：重费米子和有机超导体。它们具有非常不同的微观物理特性。该项目的目标是确定这些材料物理性质的共同趋势，以及探索新相的物理性质。特别注意的是不连续和连续的量子相变附近，其中定性和定量的影响，由变化的量的混乱进行了检查。压力是调节系统基态的主要手段。该项目在测量设计和执行课程中培养了两名研究生。计划在2002-2003学年为研究生开设一门磁共振课程。较小的技术项目，既针对特定的实验，也针对一般的实验室改进，被分配给本科生。在目前人们感兴趣的许多材料中，电子的行为是相关的。材料的电行为或状态取决于哪一种涉及电子的相互作用占主导地位。本课程中的一些材料具有与这些相互作用相关的特性，这些特性在技术上是有用的，即在相对较高的温度下没有电阻，或者在对磁场的电阻中有很大的响应。通常，稳定的状态是由外部参数控制的，如电荷掺杂、高压、高磁场等。在这个项目中，实验技术的组合，虽然主要是固态磁共振，被用来增加对相关电子系统中竞争状态的理解。重点是新相的物理性质，以及无序对这些材料的影响。所研究的系统分为两类：有机超导体和重费米子材料。通过压力和磁场实现调谐；无序是通过化学取代引入的。目标是在努力中使用控制障碍来分类转变，并理解由障碍引起的物理性质的定性变化，有时是戏剧性的变化。该项目在测量设计和执行课程中培养了两名研究生。计划在2002-2003学年为研究生开设一门磁共振课程。较小的技术项目，既针对特定的实验，也针对一般的实验室改进，被分配给本科生。

This project involves the application of solid state magnetic resonance techniques to address current questions related to competing ground states in selected correlated electron systems. The approach is based on the examination of several materials where antiferromagnetism competes with a paramagnetic Fermi Liquid phase (and possibly superconductivity) or a Spin-Peierls phase. The materials under study are from two families: heavy fermion and organic superconductors. They are characterized by very different microscopic physics. The goal of the project is to identify common trends in the physical properties of these materials, as well as to explore the physical properties of novel phases. Particular attention is paid to the vicinity of discontinuous and continuous quantum phase transitions, where the qualitative and quantitative effects resulting from varying the amount of disorder is examined. Pressure is the predominate means used to tune the ground state of the systems in question. The project trains two graduate students in the course of measurement design and execution. A course in magnetic resonance for the graduate level is planned for the 2002-2003 academic year. Smaller technical projects, both specific to particular experiments and for general laboratory improvements, are assigned to undergraduates.In a number of materials of current interest, the electrons behave in a correlated manner. The electrical behavior, or state, of the material depends upon which interaction involving the electrons dominates. Some of the materials in this class have properties related to these interactions that are technologically useful, i.e. no electrical resistance at relatively high temperatures or a large response in the electrical resistance to magnetic fields. Typically, the state that is stabilized is controlled by external parameters such as charge doping, high pressure, high magnetic fields, and so on. In this project, a combination of experimental techniques, though primarily solid state magnetic resonance, are used to gain an increased understanding of the competing states in correlated electron systems. The emphasis is on the physical properties of novel phases, and the effects of disorder on these materials. The systems investigated fall into two classes: organic superconductors and heavy fermion materials. Tuning is achieved with pressure and magnetic field; disorder is introduced through chemical substitution. The goal is to use controlled disorder in the efforts to classify transitions, and also to understand the qualitative, and sometimes dramatic, changes in the physical properties induced by the disorder. The project trains two graduate students in the course of measurement design and execution. A course in magnetic resonance for the graduate level is planned for the 2002-2003 academic year. Smaller technical projects, both specific to particular experiments and for general laboratory improvements, are assigned to undergraduates.