Zaytseva Iryna, Abaloszew Aleksander, Camargo Bruno C, Syryanyy Yevgen, Cieplak Marta Z
Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, 02668, Warsaw, Poland.
Sci Rep. 2020 Nov 4;10(1):19062. doi: 10.1038/s41598-020-75968-9.
Recent studies suggest that in disordered ultrathin films superconducting (SC) state may be intrinsically inhomogeneous. Here we investigate the nature of SC state in ultrathin Nb films, of thickness d ranging from 1.2 to 20 nm, which undergo a transition from amorphous to polycrystalline structure at the thickness [Formula: see text] nm. We show that the properties of SC state are very different in polycrystalline and amorphous films. The upper critical field ([Formula: see text]) is orbitally limited in the first case, and paramagnetically limited in the latter. The magnetic field induced superconductor-metal transition is observed, with the critical field approximately constant or decreasing as a power-law with the film conductance in polycrystalline or amorphous films, respectively. The scaling analysis indicates distinct scaling exponents in these two types of films. Negative contribution of the SC fluctuations to conductivity exists above [Formula: see text], particularly pronounced in amorphous films, signaling the presence of fluctuating Cooper pairs. These observations suggest the development of local inhomogeneities in the amorphous films, in the form of proximity-coupled SC islands. An usual evolution of SC correlations on cooling is observed in amorphous films, likely related to the effect of quantum fluctuations on the proximity-induced phase coherence.
最近的研究表明，在无序超薄薄膜中，超导（SC）态可能本质上是不均匀的。在此，我们研究了厚度d在1.2至20纳米范围内的超薄铌薄膜中SC态的性质，这些薄膜在厚度[公式：见正文]纳米时会从非晶态转变为多晶态结构。我们表明，SC态的性质在多晶薄膜和非晶薄膜中非常不同。在第一种情况下，上临界场（[公式：见正文]）受轨道限制，而在后者中受顺磁限制。观察到磁场诱导的超导体 - 金属转变，在多晶或非晶薄膜中，临界场分别大致恒定或随着薄膜电导率以幂律形式下降。标度分析表明这两种类型的薄膜具有不同的标度指数。在[公式：见正文]以上，SC涨落对电导率存在负贡献，在非晶薄膜中尤为明显，这表明存在波动的库珀对。这些观察结果表明，非晶薄膜中存在以近邻耦合SC岛形式出现的局部不均匀性。在非晶薄膜中观察到冷却时SC关联的通常演化，这可能与量子涨落对近邻诱导相位相干的影响有关。
