Quantum Phase Transitions in Spin Systems

本基金的主要目的是对量子自旋系统的有限温带性质进行系统的理论研究。该项目汇集了来自显然不同系统的各种各样的问题。例如，铜化合物，也被称为高Tc超导体，在低掺杂水平下表现出反铁磁波动和淬火无序之间复杂的相互作用。量子霍尔效应系统中的核磁共振显示出新的自旋相关性。除了这些主要的例子外，稀土金属间化合物的磁性基态也受到无序或竞争能量尺度的严重影响。最后是各向异性材料，其中自旋交换和传导主要沿着一个方向发生。所有这些工作都将在量子场理论的框架内进行，该理论来源于对自旋的连续描述。高Tc超导性的发现所引起的风暴很早就解决了一个老问题，即量子反铁磁体的问题。PI负责一些主要的发展，现在提议将这项工作扩展到其他各种问题，特别是涉及有限温度效应的问题。这些应用是在轻掺杂的化合物（这表明磁性是如何被掺杂破坏的）和它们的温度依赖特性中。＊＊＊

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. ***