Revealing the magnetic proximity effect in EuS/Al bilayers through superconducting tunneling spectroscopy
Revealing the magnetic proximity effect in EuS/Al bilayers through superconducting tunneling spectroscopy
复制标题
通过超导隧道光谱揭示 EuS/Al 双层中的磁邻近效应
DOI：
10.1103/physrevmaterials.1.054402
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发表时间：
2017
影响因子：
3.4
通讯作者：
Giazotto, F.
中科院分区：
文献类型：
--
作者：
Strambini, E.;Golovach, V. N.;De Simoni, G.;Moodera, J. S.;Bergeret, F. S.;Giazotto, F.
铁磁绝缘体与超导体接触会引起Bardeen-Cooper-Schrieffer（BCS）态密度（DoS）奇异性的交换分裂。分裂的幅度与穿透到超导体中的深度与超导相干长度相当的交换场成比例，并且其幅度范围从几特斯拉到几十特斯拉。我们研究了EuS/Al双层膜中的磁邻近效应，并表明EuS的畴结构影响交换分裂BCS峰的位置和线形。值得注意的是，即使在EuS层的未磁化状态下也观察到明显的交换分裂，这表明EuS的畴大小与超导相干长度相当。在磁化EuS层时，分裂增加，而峰改变形状。电导测量作为偏置电压的函数，在最低温度下，使我们能够与分裂BCS DoS的线形状的特征域结构中的EuS层。这些结果铺平了道路工程三重态超导相关的畴壁EuS/Al双层膜。此外，在我们的隧穿光谱测量中观察到的硬间隙和大分裂使EuS/Al成为在研究Majorana束缚态的实验中替代强磁场的优秀候选者。
A ferromagnetic insulator in contact with a superconductor is known to induce an exchange splitting of the singularity in the Bardeen-Cooper-Schrieffer (BCS) density of states (DoS). The magnitude of the splitting is proportional to the exchange field that penetrates into the superconductor to a depth comparable with the superconducting coherence length and which ranges in magnitude from a few to a few tens of tesla. We study this magnetic proximity effect in EuS/Al bilayers and show that the domain structure of the EuS affects the positions and the line shapes of the exchange-split BCS peaks. Remarkably, a clear exchange splitting is observed even in the unmagnetized state of the EuS layer, suggesting that the domain size of the EuS is comparable with the superconducting coherence length. Upon magnetizing the EuS layer, the splitting increases while the peaks change shape. Conductance measurements as a function of bias voltage at the lowest temperatures allowed us to relate the line shape of the split BCS DoS to the characteristic domain structure in the ultrathin EuS layer. These results pave the way to engineering triplet superconducting correlations at domain walls in EuS/Al bilayers. Furthermore, the hard gap and large splitting observed in our tunneling spectroscopy measurements make EuS/Al an excellent candidate for substituting strong magnetic fields in experiments studying Majorana bound states.