NMR Studies of Field-Induced Phases and Phase Transitions

非技术摘要超导可能是宏观层面上表现出的最广为人知的水量子力学现象的例子。超导状态的物理性质是壮观的，包括电流的流动而没有损耗，以及从超导样品内部排出磁通。这些相同的性质使超导性在许多应用中独一无二地有用。重要的科学和技术重要性是了解超导是如何在强磁场中存活的。许多年前，人们预测这是可能的，因为它在微观水平上产生了一种不均匀的物质状态。在这个项目中，磁共振技术将被用来研究有证据在高场下形成新相的超导系统，包括探索它们的物理性质，目的是识别不均匀相并表征其性质。这项工作将通过研究一类磁绝缘体中的新形式的场感应磁态来补充。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局部环境很敏感。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很强的磁场。本科生将帮助设计和建造特定的部件。技术摘要将使用核磁共振技术研究超导体和量子自旋系统中由大磁场稳定的磁场感应相的性质。在超导体的情况下，材料是具有高度各向异性超导性质的有机超导体，这削弱了轨道对破裂。每一种情况下都有明显的高场相存在，这使它们成为非均匀超导的极佳候选者，这种形式在40年前就被预测过，但尚未得到证实，其性质仍未得到实验测试。磁共振很容易适应必要的极端条件，而且它对不均质性具有局部敏感性。量子自旋二聚体系统是ANS=1系统，其中二聚体位于层状六方晶格上，热力学测量证明了随着场在T1K温度变化而发生的多个相变公式。研究生将设计和实施实验计划，并得到本科生的帮助，他们将学习如何设计特定的部件。将寻找非均匀状态的证据，从中有望出现新的量子效应。

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.