Magnetic Properties of Molecular and Rutheno-Cuprate Superconductors

这个个人研究者奖是颁给波士顿学院的一位教授，他的实验研究项目集中在两类低维系统的电磁和热力学性质上，在这两类系统中，超导性和磁性相互竞争，甚至共存。这些性质将在低温和强磁场下进行研究。在一种情况下，将寻求线性链分子导体（TMTSF）超导态配对对称性的关键信息。先前的研究提供了强有力的证据，证明这些材料的超导相与反铁磁自旋密度波密切竞争，是p波三重态超导体。如果是这样，那么就没有塞曼对断裂机制来破坏磁场中的超导性。此外，存在轨道对破断效应可以减少或消除的可能性，这意味着超导状态将持续到极高的场。在本项目中，一名博士后和两名研究生将参与将先前的工作扩展到比先前工作高50%的领域和1/5的温度，以寻找三重态配对和可重入超导的明确证据。在第二种情况下，钌酸盐-铜酸盐混合磁性超导体系，也存在高场超导的可能性，但可能是通过不同的机制。这些材料具有交替的超导和反铁磁层（具有弱铁磁有序），为测试磁性和超导两种破对称状态之间的对抗关系提供了独特的环境。实验将在波士顿学院的一个新实验室设施中进行，该实验室有几个新的高磁场磁铁和稀释冰箱。参与这个项目的学生将学习技术，为他们在学术、政府或工业研究领域的职位做准备。人们早就知道，磁性会破坏所有的超导性。例如，为现代核磁共振成像仪提供动力的超导磁体在强度（因此灵敏度和分辨率）上是有限的，因为在磁体绕组中产生的磁场会削弱导线携带电流的能力。然而，也许有办法绕过超导体的这种自杀倾向。在某些低维几何形状中，即超导电子被限制在平面（如一本书的书页）甚至单个链（如一页上的线条）的情况下，超导状态有可能恢复其强度，并在远远超出常规预期的领域中持续存在。波士顿学院的一位教授获得了个人研究者奖，因为他的研究项目将在某些低维材料中研究这种可能性，在这些材料中，先前的工作（所谓的“分子超导体”）显示出在强磁场中增强超导性的令人兴奋的趋势。事实证明，这些材料是超导性和磁性在纳米尺度上相互“竞争”的材料，这一事实可能对实现高场超导性以及最终制造超高场磁铁很重要。参与该项目的研究生和博士后将学习为他们在学术、政府或工业研究岗位做准备的技术

This individual investigator award is to a professor at Boston College for an experimental research project that focuses on the electromagnetic and thermodynamic properties of two classes of low dimensional systems in which superconductivity and magnetism compete, or even coexist. These properties will be investigated at low temperatures and high magnetic fields. In one case, critical information on the pairing symmetry in the superconducting state of linear chain molecular conductors (TMTSF)_X will be sought. Previous research has provided strong evidence that these materials, whose superconducting phase is in close competition with an antiferromagnetic spin density wave, are p-wave triplet superconductors. If so, then there would be no Zeeman pair-breaking mechanism to destroy superconductivity in a magnetic field. In addition, there exists the possibility that the orbital pair-breaking effect can be reduced or eliminated, which means that the superconducting state would persist to extremely high fields. In this project, one post-doc and two graduate students will be involved in extending previous work to 50% higher field and 1/5th the temperature of previous efforts, in search of definitive evidence for triplet pairing and reentrant superconductivity. In the second case, the hybrid ruthenate-cuprate magnetic superconducting system, a possibility also exists for high field superconductivity, but perhaps by a different mechanism. These materials have alternating superconducting and antiferromagnetic (with weak ferromagnetic order) layers, providing a unique setting to test the antagonistic relationship between the two broken symmetry states of magnetism and superconductivity. The experiments will be performed in a new laboratory facility at Boston College housing several new high field magnets and dilution refrigerators. The students involved in this project will learn techniques that will prepare them for positions in academic, governmental, or industrial research.%%%It has long been established that magnetism destroys all superconductivity. For example, the superconducting magnets that power modern MRI machines are limited in strength (and thus sensitivity and resolution) due to the fact that the very field created in the magnet's windings diminishes the wire's ability to carry current. There may be ways around this suicidal tendency of superconductors, however. In certain low dimensional geometries, namely in situations where the superconducting electrons are confined to planes (like the pages of a book) or even individual chains (like the lines on a page), the possibility exists for the superconducting state to regain its strength, and to persist in fields well beyond conventional expectations. This individual investigator award to a professor at Boston College is for a project that will investigate this possibility in certain low dimensional materials, where previous work (on so-called "molecular superconductors") has shown an exciting tendency for enhanced superconductivity in very strong magnetic fields. It turns out that these materials are ones in which superconductivity and magnetism "compete" against each other on a nanoscopic scale, a fact that may prove important in the realization of high field superconductivity and, eventually, the fabrication of ultra-high field magnets. The graduate student and postdoc involved in this project will learn techniques that will prepare them for positions in academic, governmental, or industrial research.***