NMR Studies of Field-Induced Phases and Phase Transitions

超导性可能是在宏观水平上表现出的量子力学现象的最广为人知的例子。超导状态的物理性质是壮观的，包括没有损耗的电流流动和从超导样品内部排出的磁通量。这些相同的性质使得超导导电性在许多应用中具有独特的用途。一个重要的科学和技术的重要性是了解超导性如何生存的高磁场。许多年前，人们预测，通过一种在微观水平上产生物质不均匀状态的机制，这是可能的，在这个项目中，磁共振技术将被用来研究超导系统，其中有证据表明在高场下形成了一个新的相，包括探索它们的物理特性，目的是识别不均匀相并确定其特性。这一工作将通过对一类磁绝缘体中新形式的场致磁态的研究来补充。磁共振适合于这种类型的问题，因为它对被探测的核自旋附近的环境很敏感。研究生将在一系列极端条件下设计和执行实验计划，包括非常低的温度和高磁场。本科生将协助设计和建造特定的组件。技术摘要超导体和量子自旋系统中磁场感应相的性质，由大磁场稳定，将使用核磁共振技术进行研究。在超导体的情况下，材料是有机超导体，具有高度各向异性的超导性质，削弱了轨道对断裂。在每种情况下都存在着不同的高场相的证据，使它们成为40年前预测但尚未证实的非均匀超导体的绝佳候选者，其性质也未经实验验证。磁共振很容易适应必要的极端条件，而且它是一种对非均匀性敏感的局部问题。量子自旋二聚体系统是一个S =1的系统，其中的二聚体坐在一个分层的六方晶格，并为热力学测量给出证据formultiple相变作为领域的变化在temperaturesT1K。研究生将设计和实施实验项目，并由本科生协助，本科生将学习如何设计特定的组件。我们将寻找非均匀态的证据，并期望从中出现新的量子效应。

non-technical abstractSuperconductivity is probably the most widely known example of aquantum mechanical phenomenon manifested at a macroscopic level.The physical properties attributed to the superconducting stateare spectacular and include the flow of electrical current withoutloss and the expulsion of magnetic flux from the interior of asuperconducting sample. These same properties makesuperconductivity uniquely useful for many applications. Ofimportant scientific and technological importance is to understandhow superconductivity survives to high magnetic fields. Many yearsago, it was predicted that this is possible through a mechanismproducing a state of matter inhomogeneous on a microscopic level.In this project, magnetic resonance techniques will be used to study superconducting systems for which there is evidence for formation of a new phase at high fields, including an exploration of their physical properties, with the aim of identifying the inhomogeneous phase and characterizing its properties. This work will be complementedby investigations of new forms of field-induced magnetic states ina class of magnetic insulators. Magnetic resonance is suitable forthis type of problem because it is sensitive to the environmentlocally proximate to the nuclear spins being probed. Graduatestudents will engineer and carry out the experimental programunder a range of extreme conditions, including very lowtemperatures and high magnetic fields. Undergraduate students willassist in the design and construction of specific components.technical abstractThe nature of magnetic field-induced phases in superconductors andquantum spin systems, stabilized by large magnetic fields, will bestudied using nuclear magnetic resonance techniques. In the caseof the superconductors, the materials are organic superconductorswith highly anisotropic superconducting properties which weakensorbital pair-breaking. Evidence exists for distinct high-fieldphases in each case, making them excellent candidates forinhomogeneous superconductivity in a form predicted forty yearsago but not yet confirmed, and for which its properties remainuntested experimentally. Magnetic resonance accommodates easilythe necessary extreme conditions, and it is a local probesensitive to inhomogeneities. The quantum spin dimer system is anS=1 system in which the dimers sit on a layered hexagonal lattice,and for which thermodynamic measurements give evidence formultiple phase transitions as the field is varied at temperaturesT1K. Graduate students will design and carry out the experimentalprogram, and are assisted by undergraduates who will learn how toengineer specific components. Evidence for inhomogeneous stateswill be looked for, from which new quantum effects are expected toemerge.