Chockalingam S P, Sarangi S, Bhat S V, Oka K, Nishihara Y
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
J Phys Condens Matter. 2009 Jan 28;21(4):045704. doi: 10.1088/0953-8984/21/4/045704. Epub 2009 Jan 8.
A new ac loss behaviour is observed in the superconducting state of Bi(2)Sr(2)CaCu(2)O(8) single crystals using a novel technique of measuring dissipation at radio frequencies. It is found that the ac loss in the superconducting state is larger than that in the normal state. This counter-intuitive result is explained in terms of the cumulative effect of repetitive decoupling of intrinsic Josephson junctions in the crystals and analysed in the framework of Ambegaokar-Baratoff theory. The ac losses are studied as a function of temperature, rf amplitude and magnetic field applied at different orientations. A peak in ac losses is observed in the superconducting state along the temperature scale. The amplitude of the peak decreases and shifts towards lower temperature with increasing field and also when the field orientation with respect to the c axis of the crystal changes from the perpendicular to parallel direction. The origin of the peak and its behaviour are discussed in the context of coupling energy of Josephson junctions present in the sample. In the presence of a magnetic field another peak in ac losses arises at temperatures close to T(c), which is associated with the Lorentz-force-driven motion of vortices.
利用一种测量射频损耗的新技术，在Bi(2)Sr(2)CaCu(2)O(8)单晶的超导态中观察到一种新的交流损耗行为。研究发现，超导态下的交流损耗大于正常态下的交流损耗。这一与直觉相悖的结果通过晶体中本征约瑟夫森结的重复解耦的累积效应来解释，并在安贝加奥卡-巴拉托夫理论的框架内进行分析。研究了交流损耗随温度、射频幅度以及不同取向施加的磁场的变化。在超导态下，沿温度范围观察到交流损耗出现一个峰值。随着磁场增加，以及当磁场相对于晶体c轴的取向从垂直方向变为平行方向时，峰值幅度减小并向低温方向移动。结合样品中存在的约瑟夫森结的耦合能量，讨论了该峰值的起源及其行为。在存在磁场的情况下，在接近T(c)的温度下会出现另一个交流损耗峰值，这与洛伦兹力驱动的涡旋运动有关。
