EXPERIMENTAL VERIFICATION AND CONTROL OF SPIN LIQUID STATE

本项目的目的是从实验上验证和控制理论上预言的某些低维磁体中由于量子自旋排斥和自旋挫挫阻效应而可能存在的自旋液态。为此，我们合成了各种模型量子系统，并应用了各种互补技术，包括先进的晶体制备，核磁共振，电子自旋共振，中子散射，μ子自旋弛豫，高场磁化以及syceptobility和比热测量，与许多其他研究小组合作。本文的主要工作如下：1）合成了S=1/2反铁磁链Cu（C_6H_7N）_2Br_2、S=1/2键交替链Cu（C_6H_7N）_2Cl_2、S=1/2自旋梯Cu_2（<12>C_5H_N_2）_2Cl_4、Cu_2（C_5H_N_2<12>）_2Br_4等模型物质; 2）研究了由S=1/2子元素组成的复合自旋体系的量子效应，例如：我们对3CuCl_2 -2dx三聚体链系统进行了800 GHz的高频ESR研究，其中三个S=1/2自旋组成的铁磁三聚体在一维反铁磁耦合。我们观察到了复合自旋的特殊行为。3）量子自旋能隙相位的控制我们探讨了在具有自旋能隙的量子单重态基态系统中，通过外加强磁场或掺杂杂质离子，诱导相变的可能性.例如，在S=2/3的二聚体系Cs_3Cr_2Cl_3中，我们观察到在三个限制场区（最高达40 T）的连续相变。

The purpose of this project is to verify experimentally and control the possible spin liquid syate which is theoretically predicted to be exist in some low dimensional magnets, due to the quantum spin ejjects and spin frustration effects. For this purpose, we synthesized a various kind of model quantum systems and applied various complementary techniques, including advanced crystal preparation, nuclear Magnetic resonance, electron spin resonance, neutron scattering, muon spin relaxation, high field magnetization as well as sysceptobility and specific heat measurements, in cooperation with many other research groups. A summary of our research is as follows.1) Synthesis of the model substances such as S=1/2 antiferromagnetic chain Cu (C_6H_7N)_2Br_2, S=1/2 bond alternating chain Cu (C_6H_7N)_2Cl_2, S=1/2 spin ladder Cu_2(C_5H_<12>N_2)_2Cl_4, Cu_2 (C_5H_<12>N_2) _2Bra_4 and so on.2) Study of quantum effects of composite spin systems composed of S=1/2 subelements.For example, we performed high-frequency ESR study up to 800GHz of trimerized chain system 3CuCI_2-2dx, in which ferromagnetic trimers consisting of three S=1/2 spins coupled antiferromagnetically in one dimension. We observed peculiar behaviors characteristic of composite spin. system with nonuniform spatial structure.3) Control of quantum spin-gappped phase.We explored the possible induced-phase transition in the quantum singlet ground state systems with spin gap by applying high magnetic field or by doping impurity ions. For example, we observed successive phase transitions at three restricted field regions up to 40T in the S=2/3 dimerized system Cs_3Cr_2Cl_3.