论文标题

纳米结构的YBA $ _2 $ cu $ _3 $ o $ $ _ {7-Δ} $从微波测量中

Intrinsic Anisotropy and Pinning Anisotropy in Nanostructured YBa$_2$Cu$_3$O$_{7-δ}$ from Microwave Measurements

论文作者

Pompeo, N., Alimenti, A, Torokhtii, K, Bartolomé, E, Palau, A, Puig, T, Augieri, A, Galluzzi, V, Mancini, A, Celentano, G, Obradors, X, Silva, E

论文摘要

各向异性是决定YBCO的磁性特性的固有因素​​,因此对许多应用产生了巨大影响。通常引入人造固定中心以减轻其效果,从而减少各向异性电气和磁性。然而,超导体的纳米工程化使各向异性本身的定量不确定:由于分层结构而引起的固有各向异性,该层次由各向异性因子$γ$量化,与由于固定而引起的其他各向异性。结果,当存在方向性(双平面,纳米棒)或各向同性缺陷时,实验各向异性因子$γ$尚未达成共识。我们在这里介绍了在非常不同的纳米结构YBCO膜中的磁场和角依赖表面阻抗的测量,该膜是通过化学途径和脉冲激光沉积生长的,具有不同的缺陷(纳米棒,双平面,纳米颗粒)。我们表明,由于有可能提取真正的各向异性通量的电阻率并正确利用角度量表,因此表面阻抗测量能够从定向固定的各向异性中脱离固有各向异性。我们在所有电影中都发现,内在各向异性$γ= 5.3 \ pm0.7 $。相比之下,固定各向异性决定了一个复杂的,富含特征和非杂物,依赖性的角景观。

Anisotropy is an intrinsic factor that dictates the magnetic properties of YBCO, thus with great impact for many applications. Artificial pinning centres are often introduced in an attempt to mitigate its effect, resulting in less anisotropic electrical and magnetic properties. However, the nanoengineering of the superconductor makes the quantification of the anisotropy itself uncertain: the intrinsic anisotropy due to the layered structure, quantified by the anisotropy factor $γ$, mixes up with the additional anisotropy due to pinning. As a consequence, there is no consensus on the experimental anisotropy factor $γ$ that can result in YBCO when directional (twin planes, nanorods) or isotropic defects are present. We present here measurements of the magnetic field and angular dependent surface impedance in very different nanostructured YBCO films, grown by chemical route and by pulsed laser deposition, with different kind of defects (nanorods, twin planes, nanoparticles). We show that the surface impedance measurements are able to disentangle the intrinsic anisotropy from the directional pinning anisotropy, thanks to the possibility to extract the true anisotropic flux--flow resistivity and by correctly exploiting the angular scaling. We find in all films that the intrinsic anisotropy $γ= 5.3\pm0.7$. By contrast, the pinning anisotropy determines a much complex, feature--rich and nonuniversal, sample--dependent angular landscape.

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