Superconductivity in layered Nb/Gd films.
Superconductivity in layered Nb/Gd films.
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层状 Nb/Gd 薄膜中的超导性。
DOI：
10.1103/physrevb.49.4053
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
H. Löhneysen
中科院分区：
文献类型：
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作者：
Christoph Strunk;C. Sürgers;Uwe Paschen;H. Löhneysen
通过电阻率和直流磁化率的测量，确定了电子束蒸发Nb/Gd/Nb三层和Nb/Gd多层膜的转变温度和临界场。对于恒定厚度d（Gd）的Gd层，我们观察到随着Nb层的厚度d（Nb）减小到临界厚度d（c），T（c）和H（c2近似-to）减小，低于临界厚度d（c），超导电性被完全破坏。平行临界场在T（c）附近主要表现出二维超导体的典型温度平方根依赖性。正如理论上预测的那样，竞争对破坏机制导致H（c parallel-to）对d（Nb）的非单调依赖。我们还研究了T（c）（d（Gd））与d（Nb）的关系，发现T（c）（d（Gd））曲线随d（Cd）的增大而减小，在d（Gd）几乎等于20埃时出现台阶状结构。为了阐明这一步骤的本质，Gd薄膜的铁磁转变是由横向磁光克尔效应确定的。长程磁序仅在d（Gd）几乎等于20埃以上，这是由于在此厚度以下形成不连续的膜。这些结果表明潜在的配对破坏机制发生了变化。
The transition temperature and the critical fields of electron-beam evaporated Nb/Gd/Nb triple layers and Nb/Gd multilayers have been determined by measurements of the electrical resistivity and the dc susceptibility. For constant thickness d(Gd) of the Gd layers, we observe a decrease of T(c) and H(c2 perpendicular-to) with decreasing thickness d(Nb) of Nb layers down to a critical thickness d(c), below which superconductivity is completely destroyed. The parallel critical fields mostly show the square-root temperature dependence near T(c), typical for two-dimensional superconductors. As predicted theoretically, competing pair-breaking mechanisms lead to a nonmonotonic dependence of H(c parallel-to) on d(Nb). We have also studied the dependence T(c)(d(Gd)) with constant d(Nb) and find a decrease of the T(c)(d(Gd)) curve with increasing d(Cd) and a steplike structure at d(Gd) almost-equal-to 20 angstrom. To clarify the nature of this step, the ferromagnetic transition of the Gd films is determined with the transverse magneto-optical Kerr effect. Long-range magnetic order is found only above d(Gd) almost-equal-to 20 angstrom, which is attributed to the formation of a discontinuous film below this thickness. These results indicate a change in the underlying pair-breaking mechanism.