Dynamics of Quantum Magnets and Superconductors

该奖项支持对复杂氧化物的磁性和电荷传输性质的实验提出的基本问题的理论研究。这项工作的目的是阐明低维关联电子系统的许多可能的基态之间的竞争，它们之间的量子相变，以及它们在有限温度下的动力学和输运性质的复杂交叉。这项工作的重点之一将是关联量子系统对非磁性杂质如锌或锂的响应。核磁共振、中子散射和隧道显微镜实验表明，这种杂质可以成为电子量子态的灵敏探测器。PI计划探索这些探测器是否能够区分为高温超导体提出的不同模型。PI最近的理论将不同实验探索的结果联系在一起，并提出了新的实验和将被研究的新的理论问题。还将研究d波超导体中集体自旋单态和自旋三态激发的能谱，这些激发与费米子S=1/2准粒子激发的耦合方式，以及它们可能与“条纹”关联的相互作用。该奖项还计划在强无序过渡金属和稀土化合物中的自旋玻璃有序以及横向量子霍尔边态之间的隧道效应等方面开展相关项目。该奖项支持对高温超导体和相关过渡金属氧化物化合物的磁性和电荷输运性质实验提出的基本问题的理论研究。该提议涉及使用像锌或锂这样的杂质作为这些系统中电子的量子态的探测器。各种实验揭示的相关电子系统的响应有望阐明这些材料中磁性和超导态的基本性质。这些态既是一个谜，也是理论和实验工作的动力，这些工作挑战了我们关于超导、磁和金属态的基本概念。拟议研究的一个统一主题涉及探索量子相变在决定高温超导体和相关过渡金属氧化物在有限温度下的宏观性质和电子激发性质方面的作用。量子相变发生在零温度下，响应于外部参数的微小变化。拟议的工作还支持凝聚态理论最新方法的研究生教育。*

This award supports theoretical research on fundamental questions raised by experiments on the magnetic and charge transport properties of complex oxide compounds. The aim of this work is to elucidate the competition between the many possible ground states of correlated electron systems in low dimensions, the quantum phase transitions between them, and the complex crossovers in their dynamic and transport properties at finite temperature. One focus of this work will be the response of correlated quantum systems to non-magnetic impurities like Zn or Li. Nuclear magnetic resonance, neutron scattering, and tunneling microscopy experiments have shown that such impurities can be sensitive probes of the quantum state of the electrons. The PI plans to explore whether these probes can distinguish among the different models proposed for high temperature superconductors. The PI's recent theories correlate the results of different experimental probes and suggest new experiments and open new theoretical issues that will be investigated. The spectrum of collective spin-singlet and spin-triplet excitations in d-wave superconductors, the manner in which these excitations couple to the fermionic S=1/2 quasiparticle excitations, and their possible interplay with "stripe" correlations will also be studied. The PI also plans to pursue related projects on spin-glass order in strongly disordered transition metal and rare earth compounds, and tunneling between lateral quantum Hall edge states.%%%This award supports theoretical research on fundamental questions raised by experiments on the magnetic and charge transport properties of high temperature superconductors and related transition metal oxide compounds. The proposal involves using impurities like Zn or Li as probes of the quantum state of the electrons in these systems. The response of the correlated electron system as revealed by a variety of experiments is expected to elucidate the fundamental nature of magnetic and superconducting states in these materials. These states are both a puzzle and a motivation for theoretical and experimental work that challenges our fundamental concepts of superconducting, magnetic, and metallic states. A unifying theme of the proposed research involves exploring the role of quantum phase transitions in determining macroscopic properties and the nature of electronic excitations in high temperature superconductors and related transition metal oxides at finite temperature. Quantum phase transitions occur at zero temperature in response to small changes in an external parameter. The proposed work also supports graduate education in state-of-the art methods in condensed matter theory.***