Spin glass and chiral glass

在具有连续自由度的受挫系统中，其组成元素之间具有相互竞争的相互作用，通常会出现新的手征自由度，这在未受挫系统中没有对应的自由度。当除了受挫外还存在猝灭的随机性时，这种手性体系的有序性有望是相当新颖的。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，特别是手性。两个主题，自旋玻璃磁体和陶瓷超导体，已经被处理过。通过对这些系统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，手性有序以空间随机的方式保持自旋或相的自由度无序的新的手性玻璃相是可能的。表征高温无序相与低温手性玻璃相之间的手性玻璃转变的临界指数与三维伊辛自旋玻璃的数值相近。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相变的“手性”机制，它可以解决关于实验观察到的自旋玻璃相变的真实性质的难题。以陶瓷超导体为例，最近的实验研究表明，铜系高T_c超导体的配对对称性已被确定为d波，是实现手性玻璃态的良好候选材料。对手性玻璃相和手性玻璃转变的可能的实验检测进行了详细的研究。事实上，已经报道了几个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.