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Novel equilibrium phase diagram and dynamics of interlayer Josephson vortices in high-T_c superconductors - computer simulation approach

高温超导体层间约瑟夫森涡旋的新颖平衡相图和动力学 - 计算机模拟方法

基本信息

批准号：
15540355
负责人：
HU Xiao
金额：
$ 1.92万
依托单位：
National Institute for Materials Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

(1) Possible phases and phase transitions of interlayer Josephson vortex-lines are explored by computer simulation and the density functional theory. In high magnetic fields where vortices reside in every layer (m=1), computer simulations reveal a novel KT phase in which the intralayer vortex correlations are quasi-long-ranged while the interlayer ones are short-ranged. This novel phase transforms into low-temperature 3D lattice phase via a 2^<nd> order phase transition and into high-temperature liquid phase via a KT transition. As the magnetic field decreases, a vortex smectic phase, which shows a short-ranged intralayer vortex correlations while the block layers with denser vortices appear in every other layers (period m=2) in a long-ranged way, is stabilized by layer pinning in materials such as YBCO, accompanied by a sequential second- and first-order transitions upon cooling. In low magnetic fields, the effect of layer pinning is suppressed drastically because of high transition t … More emperature and large discrepancy between the wave-length of layer pinning and the vortex lattice constant, which naturally recovers the anisotropy scaling of melting line. These results are reported in many international conferences as invited talks, and attracting considerable attentions. Experiments designed for testing these theoretical results are scheduled in Europe, USA and Japan.(2) By means of computer simulation we find that when the angle between the magnetic field and the ab plane is not so large the distorted triangular lattice of Josephson vortices dominates the system such that pancake vortices look like to sit on chains as observed in experiment. As the tilt angle increases, the flux lines are aligned essentially in the same way as Abrikosov vortex lattice. There is a first-order phase transition between the two structures.(3) Combining group theoretical analysis of the hexagonal system with energetics based on fermiology, we found within a single band picture, that among the likely pairing states is a novel chiral spin-triplet state, which takes advantage of the nesting among different segments of the Fermi surface. This is similar to the pairing mechanism proposed for the tetragonal material SrRuO_4, though the hexagonal case would benefit further from the nesting effect. More recent developments incorporate orbital effects. There again, the physical picture of pairing induced by scattering between Fermi segments, resulting in a triplet state continues to be an important possibility pursued both experimentally and theoretically. Less

(1)用计算机模拟和密度泛函理论探讨了层间约瑟夫森涡旋线的可能相和相变。在高磁场中，涡旋驻留在每一层（m=1），计算机模拟揭示了一个新的KT阶段，其中层内涡旋相关是准长程的，而层间的短程。这种新相通过2阶相变转变为低温3D晶格相<nd>，通过KT相变转变为高温液相。随着磁场的减小，涡旋近晶相，这表明了一个短范围的层内涡旋的相关性，而密集的涡旋块层出现在每隔一层（周期m=2）在一个长范围的方式，是稳定的层钉扎在材料，如YBCO，伴随着一个连续的二阶和一阶的转变冷却。在低磁场下，由于高的相变温度，层钉扎效应被大大抑制 ...更多信息层钉扎的波长与涡旋晶格常数之间存在较大的差异，这自然恢复了熔化线的各向异性标度。这些成果在许多国际会议上作为特邀报告发表，引起了广泛的关注。为检验这些理论结果而设计的实验计划在欧洲、美国和日本进行。(2)通过计算机模拟，我们发现当磁场与ab平面的夹角不是很大时，系统中的Josephson涡的畸变三角晶格占主导地位，如实验中所观察到的那样，煎饼涡看起来像是坐在链上。随着倾斜角的增加，通量线的排列方式基本上与Abrikosov涡旋晶格相同。两种结构之间存在一级相变。(3)结合群论分析的六角系统的热力学基础上的费米，我们发现在一个单一的带图片，其中可能的配对状态是一种新的手性自旋三重态，它利用了费米面的不同部分之间的嵌套。这类似于对四方晶系SrRuO_4提出的配对机制，尽管六方晶系的情况将进一步受益于嵌套效应。最近的发展包括轨道效应。在那里，费米段之间的散射导致的配对的物理图像，导致三重态仍然是实验和理论上追求的重要可能性。少