Quantum Phase Transitions in Spin Systems

9623181 Sachdev这项拨款的主要目标是对量子自旋系统的有限温度性质进行系统的理论研究。该项目汇集了来自明显不同系统的各种问题。例如，铜酸盐化合物，也被称为高T_c超导体，在低掺杂水平下，表现出反铁磁波动和猝灭无序之间的复杂相互作用。量子霍尔效应系统中的核磁共振显示了新的自旋关联。除了这些主要的例子，还有稀土金属间化合物的性质，其中磁性基态受到无序或竞争能量尺度的严重影响。最后，在各向异性材料中，自旋交换和传导主要沿一个方向发生。所有这些工作都将在量子场论的框架下进行，量子场论源于对自旋的连续描述。高T_c超导电性的发现所产生的风暴很早就解决了一个老问题--量子反铁磁体。PI负责了一些主要的发展，现在正提议将这项工作扩展到各种其他问题，特别是涉及有限的温度效应。应用于轻掺杂化合物(这表明磁性是如何被掺杂破坏的)及其与温度有关的性质。***

9623181 Sachdev The primary objective in this grant is to undertake a systematic theoretical study of the finite temperate properties of quantum spin systems. The project brings together a wide variety of problems from apparently diverse systems. For example the cuprate compounds, also known as high Tc superconductors, at low doping levels manifest complicated interplay between antiferromagnetic fluctuations and quenched disorder. NMR in Quantum Hall effect systems shows novel spin correlations. Apart from these principal examples, there are properties of rare earth intermetallics where the magnetic ground states are critically influenced by disorder or competing energy scales. Finally there are anisotropic materials where spin exchange and conduction occur primarily along one direction. All of this work will be carried out in the framework of a quantum field theory, derived from a continuum description of the spins. %%% The storm generated by the discovery of high Tc superconductivity led, rather early, to the solution of an old problem, that of quantum antiferromagnets. The PI was responsible for some of the major developments and is now proposing to extend that work to a variety of other problems, specifically involving finite temperature effects. The applications are in lightly doped compounds (which show how magnetism is destroyed by doping) and their temperature dependent properties. ***