CONTROL OF STRONGLY CORRELATED 1D CHAIN COMPOUNDS DOPED WITH CHARGE CARRIERS

本计画的目的是探讨一维自旋液体中的奇异量子电子相。Tomonaga-Luttinger液体可以实现吗？通过引入外部刺激，是否会导致剧烈的相变？在此基础上，我们研究了铜酸盐YBa_2Cu_4O_8。YBa_2Cu_4O_8的独特之处在于它的一维双链具有明显的金属性，可以看作是一种掺杂的一维反铁磁体。通过仔细研究金属双链的输运性质，我们发现了一种新的现象--磁场诱导的维度交叉。通过施加磁场，链间输运开关从金属到绝缘附近的临界磁场B=15 T，表明电子被限制在链内。基于列别德和戈尔科夫讨论的真实的空间轨道图像，我们提出了这种转换背后的微观机制。通过考察Zn杂质的影响，给出了真实的空间轨道图像的实验验证，并在项目的最后阶段，尝试将掺杂自旋液体的思想从一维磁体推广到三维磁体。我们专注于三维自旋液体实现的几何挫折和探索奇异的现象产生的电荷载流子掺杂。作为结果，我们建立了LiV_2O_4尖晶石中重费米子态的存在，揭示了重电子质量与几何阻挫产生的自旋液态之间的密切联系。

This project aims to explore exotic quantum electronic phase in 1 dimensional spin liquids doped with charge carriers. Can Tomonaga-Luttinger liquid be realized ? By introducing external stimulation, can drastic phase change be brought about? With these in mind, we have investigated a cuprate YBa_2Cu_4O_8. YBa_2Cu_4O_8 is unique in that its 1D double chain is remarkably metallic and can be regarded as a doped 1D antiferromagnet. By carefully examining the tranport properties of the metallic double chain, we found novel phenomenon-magnetic field induced dimensional crossover. By applying magnetic field, the interchain transport switches from metallic to insulating around a critical magnetic field B=15 T, indicating electrons are confined within chains. We have proposed a microscopic mechanism behind this switching, based on a real space orbit picture discussed by Lebed and Gorkov. By examining the influence of Zn impurity, then, we have given an experimental verification of the real space orbit picture.In the last stage of the project, we have attempted to extend the idea of doped spin liquid from 1D magnet to 3D magnet. We focused on 3D spin liquid realized by a geometrical frustration and explored exotic phenomena produced by charge carrier doping. As an output, we have established the existence of a heavy fermion state in LiV_2O_4 spinel and revealed the intimate connection between the the heavy electron mass and the spin liquid state produced by geometrical frustration.