Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales.
Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales.
复制标题
具有两个排斥长度尺度的涡旋系统中的自发对称性破坏。
DOI：
10.1038/srep15569
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发表时间：
2015-10-23
影响因子：
4.6
通讯作者：
Bending SJ
中科院分区：
文献类型：
--
作者：
Curran PJ;Desoky WM;Milosević MV;Chaves A;Laloë JB;Moodera JS;Bending SJ
利用扫描霍尔探针显微镜（SHPM）研究了超导体MgB_2外延薄膜中的涡旋结构。在MgB 2单晶中观察到的不寻常的涡旋图案以前被归因于在这两个带超导体中短程排斥和长程吸引涡旋-涡旋相互作用之间的竞争; 1.5型超导方案。我们的薄膜具有比大块单晶高得多的无序度，因此这两种超导凝聚体都有望被推入具有纯粹排斥性涡旋相互作用的2型区域。我们观察到破缺对称涡旋图案在低场在所有样品后，从上述Tc场冷却。这些是一致的，在不同的长度尺度上的竞争排斥系统中看到的，非常相似的结构再现在肮脏的两个频带金斯堡-朗道计算，其中的模拟参数已被定义的实验观察。这表明，在我们的肮脏的MgB 2薄膜中，涡旋结构的对称性被破坏的涡旋排斥的存在与两个不同的长度尺度，起源于两个不同的超导冷凝。这代表了超导涡旋系统中自发对称破缺的一种全新机制，对钉扎现象和高电流密度应用具有重要意义。
Scanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our films have much higher levels of disorder than bulk single crystals and therefore both superconducting condensates are expected to be pushed deep into the type 2 regime with purely repulsive vortex interactions. We observe broken symmetry vortex patterns at low fields in all samples after field-cooling from above Tc. These are consistent with those seen in systems with competing repulsions on disparate length scales, and remarkably similar structures are reproduced in dirty two band Ginzburg-Landau calculations, where the simulation parameters have been defined by experimental observations. This suggests that in our dirty MgB2 films, the symmetry of the vortex structures is broken by the presence of vortex repulsions with two different lengthscales, originating from the two distinct superconducting condensates. This represents an entirely new mechanism for spontaneous symmetry breaking in systems of superconducting vortices, with important implications for pinning phenomena and high current density applications.