Bi-2212小台面结构中同相磁通态的几何约束稳定
Stabilization of in-phase fluxon state by geometrical confinement in small Bi-2212 mesa structures
摘要：
同相（矩形）磁通晶格是实现堆叠约瑟夫森结的相干太赫兹辐射所必需的。不幸的是，它通常是不稳定的，由于相互排斥的磁通子在相邻的结，这有利于异相（三角形）晶格。在这里，我们实验研究磁场调制的临界电流在小的Bi-2212台面结构具有不同的尺寸。当磁场严格平行于超导CuO平面时，观察到明显的类夫琅和费调制。对于长台面，调制的周期性等于每个本征约瑟夫森结的通量量子的一半，对应于三角形通量晶格。然而，通过减小台面的长度和增加磁场，周期性被改变为一个通量量子，这是矩形通量晶格的特征。因此，我们证明了在小的Bi-2212台面结构中，通过几何限制可以有效地稳定静止的同相通量态。
英文摘要：
The in-phase (rectangular) fluxon lattice is required for achieving coherent THz emission from stacked Josephson junctions. Unfortunately, it is usually unstable due to mutual repulsion of fluxons in neighbor junctions, which favors the out-of-phase (triangular) lattice. Here we experimentally study magnetic field modulation of the critical current in small Bi-2212 mesa structures with different sizes. A clear Fraunhofer-like modulation is observed when the field is aligned strictly parallel to superconducting CuO planes. For long mesas the periodicity of modulation is equal to half the flux quantum per intrinsic Josephson junction, corresponding to the triangular fluxon lattice. However, the periodicity is changed to one flux quantum, characteristic to the rectangular fluxon lattice, both by decreasing the length of the mesas and by increasing magnetic field. Thus, we demonstrate that the stationary in-phase fluxon state can be effectively stabilized by geometrical confinement in small Bi-2212 mesa structures.
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