ENDOR and Optical Studies of Fractional S = 1/2 Spins and Haldane Gap in S = 1 Antiferromagnetic Linear Chains

这项研究涉及一个扩展系列的EPR和光学 在各种情况下对S=1线性反铁磁链的实验 不同的材料。 这些链在闭合时有一个单线态 基态和在其激发光谱中的间隙（Halfenite gap）代表了当前对量子力学的强烈兴趣。 无序基态 开链具有非常新颖的性质， 显示分数自旋，S=1/2，（自旋子）在链端。 电子-核双共振（ENDOR）将用于绘制 自旋1/2的空间分布的网站延伸， 从链条的末端。 链条断裂导致两端开口 将通过替换少量的非- 磁性离子的Ni离子（S=1）在各种有机和 含镍链的无机化合物。 还将努力 通过光学泵浦一些镍离子来产生这些链断裂 脱离基态 通过这种方式，可以改变链长 通过改变光的强度和自旋子之间的相互作用 可以观察到。 此外，拉曼散射正在进行， 弗朗西斯比特实验室的合作者们测量了Half-gap 在k=0时，帮助解决一些重要问题， 其性质和大小相对于k=.处的差距。 %%% 化合物的磁性，其中磁性中心 排列成链， chains表示一个前沿主题的交集， 理论磁性与创造性的材料合成。 直到 最近这种理想的链状化合物并不存在 很难保持磁链足够远， 链之间的相互作用，最终导致三个 维磁行为 然而，新材料已经 近年来合成的，显示了这个理想的一个- 维磁行为 首席研究员的工作 与AT T贝尔实验室的材料科学家密切合作， 为上面提到的实验创造这些材料。 它 希望通过对这些一维的理解， 系统将导致进一步深入了解二维系统 并延伸到高温超导性。

This research involves an extended series of EPR and optical experiments on S=1 linear antiferromagnetic chains in a variety of different materials. These chains which when closed have a singlet ground state and a gap in their excitation spectrum (the Haldane gap) are representative of the strong current interest in quantum disordered ground states. Open chains have the very novel property of displaying fractional spin, S=1/2, (spinons) at the chain ends. Electron- nuclear double resonance (ENDOR) will be used to map out the spatial distribution of the spin 1/2 on the sites extending in from the chain ends. Breaks in the chains and resulting open ends with spinons will be created by substituting small amounts of non- magnetic ions for the Ni ions(S=1) in a variety of organic and inorganic compounds with Ni chains. Efforts will also be made to create these chain breaks by optically pumping some of the Ni ions out of their ground state. In this way chain lengths can be varied by changing the light intensity and interaction between the spinons may be observed. In addition Raman scattering is underway with collaborators at The Francis Bitter lab to measure the Haldane gap at k=0 to help resolve some of the important questions involving its nature and magnitude relative to the gap at k=.. %%% The magnetic behavior of compounds in which the magnetic centers are arrayed in chains with negligible interaction between the chains represents an intersection of a forefront topic in theoretical magnetism with creative materials synthesis. Until recently such ideal chain compounds did not exist as it was difficult to keep the magnetic chains far enough apart to inhibit interaction among the chains, ultimately resulting in three dimensional magnetic behavior. However, new materials have been synthesized in recent years which display this ideal one- dimensional magnetic behavior. The principal investigator works closely with materials scientists at AT&T Bell Laboratories who are creating these materials for the experiments mentioned above. It is hoped that an enhanced understanding of these one dimensional systems will lead to further insight into two-dimensional systems and by extension to high temperature superconductivity.