Spin glass and chiral glass

在具有连续自由度的受挫系统中，组成元素之间存在竞争相互作用，新的“手性”自由度经常出现，而在未受挫系统中没有对应的自由度。当除挫折外还存在淬灭随机性时，这种手性体系的有序性质将是非常新颖的。本研究的目的是通过广泛的蒙特卡罗模拟来研究随机受挫系统的相变，特别注意手性。两个主题，自旋玻璃磁体和陶瓷超导体，已经处理。通过对这些体系的标准模型进行大规模的蒙特卡罗模拟，我们已经证明了在适当的条件下，一种新的手性玻璃相是可能的，其中手性顺序在空间随机的方式下保持自旋或相自由度的无序。表征手性玻璃在高温无序相和低温手性玻璃相之间转变的临界指数与三维Ising自旋玻璃的值接近。在自旋玻璃磁体的情况下，基于手性-玻璃有序的数值发现，提出了一种新的自旋-玻璃转变的“手性”机制，这可以解决有关实验观察到的自旋-玻璃转变的真实性质的难题。在陶瓷超导体中，铜高t_c超导体是实现手性玻璃态的良好候选材料，其配对对称性通过最近的实验研究已经确定为d波。对所提出的手性玻璃相和手性玻璃转变的可能实验检测进行了详细的研究。事实上，已经有几个实验结果部分支持手性玻璃态。

In Frustrated systems with continuous degrees of freedom, which have competing interaction between constituent elements, new 'chiral' degrees of freedom often appear which has no counterpart in unfrustrated systems. When there exists quenched randomess in addition to frustration, the ordering properties of such chiral system are expected to be quite novel. The purpose of the present study has been to investigate the phase transition of randomly frustrated systems with particular attention to the chirality by means of extensive Monte Carlo simulations. Two subjects, spin-glass magnets and ceramic superconductors, have been dealed with. By performing large-scale Monte Carlo simulations on the standard models for these systems, we have shown that a new chiral-glass phase, where the chirality orders in a spatially random manner with preserving the spin or the phase degrees of freedom disordered, is possible under appropriate conditions. Critical exponents characterizing the chiral-glass transition between the high-temperature disordered phase and the low-temperature chiral-glass phase are found to be close to the values of the three-dimensional Ising spin glass. In the case of spin-glass magnets, a new 'chirality' mechanism of the spin-glass transition has been proposed based on the numerical finding of the chiral-glass ordering, which could resolve the puzzle concerning the true nature of the experimentally observed spin-glass transitions. In the case of ceramic superconductors, it is shown that cuprate high-T_c superconductors, whose pairing symmetry has been established to be d-wave via recent experimental strudies, are good candidate materials to realize the chiral-glass state. Possible experimental detection of the proposed chiral-glass phase and the chiral-glass transition is examined in detail. In fact, several experimental results which partly support the chiral-glass state were already reported.