Vortex dynamics in the intrinsic Josephson junction near the quantum regime

高度各向异性的高tc超导体，如Bi: 2212，可以看作是由Josephson相互作用耦合的超导CuO_2层堆叠。在用传统低tc材料制成的单约瑟夫森结中发现了一些从未观察到的特性，这些特性与超导层的多层结构和原子厚度有关。特别是，涡旋相图和HTSC在平行于层的强磁场存在下的相关电磁特性已经成为最近激烈的实验和理论研究的主题。在本项目中，我们报道了Bi: 2212堆叠结Josephson通量流态中Shapiro阶跃的首次观察。当在强平行磁场中微波频率照射结时，当外部微波频率与约瑟夫森频率谐波相关时，直流电流-电压特性中电流急剧增加。约瑟夫森通量流态中夏皮罗阶跃的存在是约瑟夫森涡晶格在整个层叠厚度上进行相干运动的有力证据。

Highly anisotropic high-Tc superconductors, such as Bi : 2212, can be considered as stacks of superconducting CuO_2 layers coupled by the Josephson interaction. Several properties which have never been observed in single Josephson junctions made from conventional low-Tc materials have been found, which are associated with the multilayer structure and with the atomic thickness of the superconducting layers. In particular, the vortex phase diagram and the related electromagnetic properties of HTSC in the presence of a strong magnetic field parallel to the layers have been the subject of recent intense experimental and theoretical studies. In this project, we report the first observation of Shapiro steps in the Josephson flux flow state of Bi : 2212 stacked junctions. When the junction is irradiated at microwave frequencies in a strong parallel magnetic field, a steep increase of the current is observed in the dc current-voltage characteristics when the external microwave frequency and the Josephson frequency are harmonically related. The existence of Shapiro steps in the Josephson flux flow state is strong evidence of coherent motion of the Josephson vortex lattice through the whole thickness of the stack.