Vortex states in micron-sized Bi2Sr2CaCu2O8+y crystals

29th International Symposium on Superconductivity

Ooi, Shuuichi^1 ; Mochiku, Takashi^1 ; Tachiki, Minoru^1 ; Hirata, Kazuto^1

National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki

305-0047, Japan^1

关键词: Intrinsic Josephson junctions (IJJs);    Melting transitions;    Oscillating behavior;    Resistance measurement;    Short coherence length;    Thermal fluctuations;    Topological defect;    Triangular lattice;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/871/1/012019/pdf
DOI  :  10.1088/1742-6596/871/1/012019

来源: IOP

【 摘 要 】

Large thermal fluctuation, owing to high superconducting transition temperature, short coherence length and quasi-two-dimensionality, brings about a rich variety of vortex phases in Bi2Sr2CaCu2O8+y(Bi2212). To study how the vortex states and the transitions would be modified when vortices are confined in a small-sized crystal, we have measured the c-axis resistance using a stack of the intrinsic Josephson junctions (IJJs) of Bi2212. In tiny Bi2212 crystals of several micron, it is possible to observe the series of vorticity transitions using the c-axis resistance measurements. Combining the observation of vorticity changes and detection of a melting transition, we found an oscillating behavior of melting transition temperatures Tmas a function of magnetic field (or number of vortices) in small squared Bi2212 with a lateral dimension of 5-10 μm. In the case of the square-shaped crystals, it seems that Tmis enhanced around the vortex numbers Nvof i2(i: integer), indicating a matching of square vortex lattices in the square boundary. However, the frustration between the square boundary shape and vortex lattice that prefers a triangular lattice complicates the situation. A deformed square lattice without topological defects is probably realized at large i2as a geometrical matching state.