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

我们围绕以下主题进行了研究，并发表了论文，包括几个特邀演讲。我们从微观能级的角度研究了含时外场下量子系统的时间演化特征。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而产生的相变和合作现象。得到了三角形晶格上类XY海森堡反铁磁体的基态相图。这些不同的相作为各向异性和外加磁场的函数出现，这归因于有限温度下量子涨落起到了热涨落的作用。我们还研究了三角形自旋管中的能隙。我们发现了磁化强度与晶格单位不符的系统。我们还研究了在量子Blume-Capel模型中一种新型的量子涨落诱导的磁序。还研究了自旋交叉材料的相变和亚稳态结构的存在。研究了强受阻系统中的慢弛豫过程，发现了一种新的慢弛豫过程，即熵诱导的慢弛豫。

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.