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

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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.