Spin glass and chiral glass

在具有连续自由度的阻挫系统中，由于组成元件之间存在相互竞争作用，经常会出现新的“手征”自由度，而这在非阻挫系统中是没有的。当除了阻挫之外还存在猝灭无规性时，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研究随机阻挫系统的相变，特别注意手性。讨论了自旋玻璃磁体和陶瓷超导体两个课题。通过对这些系统的标准模型进行大规模蒙特卡罗模拟，我们已经证明了一种新的手征玻璃相，在适当的条件下，在空间随机的方式保持自旋或相位自由度无序的手征顺序是可能的。表征高温无序相和低温手性玻璃相之间的手性玻璃转变的临界指数被发现接近三维伊辛自旋玻璃的值。在自旋玻璃磁体的情况下，一个新的“手性”机制的自旋玻璃转变已被提出的基础上的手征玻璃有序的数值发现，这可能解决的难题有关的真实性质的实验观察到的自旋玻璃转变。在陶瓷超导体的情况下，铜氧化物高温超导体是实现手征玻璃态的良好候选材料，其对对称性已被最近的实验研究确定为d波。可能的实验检测建议的手性玻璃相和手性玻璃化转变进行了详细研究。事实上，已经报道了一些部分支持手性玻璃态的实验结果。

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.