Abstract The influence of structural defects on superconducting properties of pure Ta was studied by the positron annihilation lifetime spectroscopy (PALS), magnetic and electrical resistivity measurements. The obtained results provide a clear evidence that the type-I superconductivity in Ta may be converted into type-II by introducing structural defects. In particular, PALS spectra measured for Ta samples indicate that two cold-rolled samples contain a high concentration of defects (mainly dislocations and vacancies associated with them). At the same time, the annealed sample is almost free of any defects. Magnetic results show that both cold-rolled samples exhibit type-II superconductivity while after annealing the Ta sample recovers type-I superconductivity. The estimated Ginzburg-Landau parameter κ from the electrical resistivity data reveals that the annealed Ta sample is the type-I superconductor with κ = 0.69 ( 1 ) which is slightly less value than the critical value of κ c = 1 / 2 . At the same time, both cold-rolled samples are type-II superconductors with κ ≈ κ c .

中文翻译：

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冷轧钽中的 II 型超导性

摘要 通过正电子湮没寿命谱（PALS）、磁电阻率和电阻率测量研究了结构缺陷对纯Ta超导性能的影响。所获得的结果提供了一个明确的证据，即可以通过引入结构缺陷将 Ta 中的 I 型超导性转化为 II 型。特别是，Ta 样品测量的 PALS 光谱表明两个冷轧样品含有高浓度的缺陷（主要是与它们相关的位错和空位）。同时，退火后的样品几乎没有任何缺陷。磁学结果表明，两种冷轧样品都表现出 II 型超导性，而 Ta 样品在退火后恢复了 I 型超导性。从电阻率数据估计的 Ginzburg-Landau 参数 κ 表明，退火的 Ta 样品是 I 型超导体，κ = 0.69 ( 1 )，其值略小于 κ c = 1 / 2 的临界值。同时，两个冷轧样品都是 κ ≈ κ c 的 II 型超导体。