Quantum mechanical response to time-dependent external field and related cooperative phenomena

本课题的研究内容和发表的论文见论文单，并进行了包括邀请演讲在内的多场演讲。从微观能级的观点出发，研究了含时外场下量子系统的时间演化特性。我们发现V15的能量结构随Dzyaloshinski-Moriya相互作用的方向而敏感地变化。利用量子主方程研究了能量耗散对磁化过程的影响。我们还研究了由于量子力学性质引起的相变和合作现象。得到了三角晶格上XY类海森堡反铁磁体的基态相图。在有限温度下，由于量子涨落起着热涨落的作用，各向异性和外磁场的作用使不同的相出现。我们还研究了三角形自旋管中的能隙。我们发现系统的磁化不适合晶格单位。在量子Blume-Capel模型中，我们还研究了一种新的量子涨落诱导的磁序。研究了自旋交叉材料的相变和亚稳结构的存在。研究了强阻挫系统中的慢弛豫过程，发现了一种新的慢弛豫类型，即熵诱导慢弛豫。

We have studied on the following theme and published papers as listed in the separated sheet and also gave talks including several invited talks.We studied characteristics of time evolution of quantum systems under time-dependent external fields from a view point of microscopic energy levels. We found that the energy structure of V15 is sensitively changes with the direction of the Dzyaloshinski-Moriya interaction. The effect of energy dissipation on the magnetization process was also studied by making use of quantum master equation. We also studied phase transition and cooperative phenomena due to quantum mechanical properties. We obtain the ground state phase diagram of XY-like Heisenberg antiferromagnets on the triangular lattice. There various phases appear as a function of anisotropy and the external magnetic field, which is attributed to the quantum fluctuation playing the role of thermal fluctuation at finite temperatures. We also studied the energy gap in the triangle spin-tube. We found systems where the magnetization does not fit with the lattice unit. We also study a new type of quantum fluctuation induced magnetic order in the quantum Blume-Capel model. The phase transition and the existence of metastable structures in the spin-crossover material were also studied. Slow relaxation processes in the strongly frustrated system were studied and found new type of slow relaxation, i.e. entropy-induced slow relaxations.