Studies on Superconducting States of Unconventional Superconductors using Local-Field Measuring Techniques

利用局域场测量技术，如磁光成像和微霍尔探头磁测量，我们阐明了非常规超导体中各种新态的详细磁性质。在高度各向异性层状超导体Bi2Sr2CaCu2O8+y中，在倾斜磁场下实现了两种涡旋共存的新型涡旋态。Pancake涡和Josephson涡是由垂直于超导平面和平行于超导平面的场分量产生的。作为双场分量的函数，实现了涡旋系统的各种基态。这些态的特征涡旋排列为“涡链”，其中煎饼涡通过它们之间的弱吸引相互作用来装饰约瑟夫森涡旋。这种相互作用也可以利用约瑟夫森涡来控制煎饼涡。我们已经通过可视化煎饼旋涡的分布证明了这种可控性。特别是涡流镜头Effe…在约瑟夫森涡旋的作用下，层状金属间化合物超导体CaAlSi显示出上临界场的反常角度依赖关系。相比之下，在一种相关的化合物CaGaSi中，上临界场通常是。通过在CaAlSi交流面上的涡旋穿透可视化，阐明了沿c轴的不均匀性的存在。Ga的掺杂逐渐抑制了这种反常的涡旋穿透。PrOs4Sb12被认为是具有时间反转对称性的三重态超导体。为了揭示与这种新的超导态相关的反常现象，我们利用微霍尔证明进行了详细的局域场测量。与另一种三重态超导体Sr2Ru04的情况类似，当局域磁感应强度改变符号时，局域场出现反常。我们现在试探性地将这种反常现象归因于具有相反手性的磁区之间存在磁区边界。较少

By using local-field measuring technique, such as magneto-optical imaging and micro-Hall probe magnetometry, we have clarified the detailed magnetic properties of various novel states in unconventional superconductors.In highly anisotropic layered superconductor Bi2Sr2CaCu2O8+y, a novel vortex state with coexisting two kinds of vortices are realized under tilted fields. Pancake vortices and Josephson vortices are generated by the field components perpendicular and parallel to the superonducting plane. As a function of two-field components, various ground states of vortex systems are realized. The characteristic vortex arrangements of these states are 'vortex chains', where pancake vortices are decorating Josephson vortices by weak attractive interaction between them. This interaction can also be utilized to control the pancake vortices using Josephson vortices. We have demonstrated such controllability by visualizing the distribution of pancake vortices. In particular, vortex lens effe … More ct, where pancake vortices are focused at the center of the sample by the help of Josephson vortices have been demonstrated for the first time.A layered intermetallic superconductor CaAlSi with AIB2 structure shows an anomalous angular dependence of the upper critical field. By contrast, in a related compound CaGaSi, the upper critical field normally. By visualizing vortex penetration on the ac plane of CaAlSi, exsistence of inhomogeneity along c-axis is clarified. Ga-doping gradually suppresses such an anomalous vortex penetration.PrOs4Sb12 is claimed to be a triplet superconductor with broken time-reversal symmetry. In order to reveal anomalies related to this novel superconducting state, we have performed detailed local field measurements using micro-Hall proves. It is found that the local field shows an anomaly when the local magnetic induction changes the sign, similar to the case of another triplet superconductor Sr2Ru04. We now tentatively ascribe such anomalies to the presence of domain boundaries between domains with opposite chiralities. Less