We have investigated the conductance spectra of Sn-Bi2Se3 interface junctions down to 250 mK and in different magnetic fields. A number of conductance anomalies were observed below the superconducting transition temperature of Sn, including a small gap different from that of Sn, and a zero-bias conductance peak growing up at lower temperatures. We discussed the possible origins of the smaller gap and the zero-bias conductance peak. These phenomena support that a proximity-effect-induced chiral superconducting phase is formed at the interface between the superconducting Sn and the strong spin-orbit coupling material Bi2Se3.
Semiclassical theory for proximity-induced superconducting systems with spin-orbit coupling
School of Physics, Sun Yat-sen University（中山大学物理学院）；Interdisciplinary Center for Theoretical Physics and Information Sciences (ICTPIS), Fudan University（复旦大学理论物理与信息科学交叉中心）；Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices, Sun Yat-sen University（中山大学广东省磁电物理与器件重点实验室）；School of Physics, University of Science and Technology of China（中国科学技术大学物理学院）
Theory of superconducting and magnetic proximity effect in S$\mid$F structures with inhomogeneous magnetization textures and spin-active interfaces
我们研究了超导体$\mid$铁磁双层中的邻近效应和逆邻近效应，并考虑了迄今为止文献中大多被忽视的几个重要因素。这些包括自旋相关的界面相移（自旋-DIPS）和非均匀的纹理中的铁磁层的磁化强度，这两者都预计将存在于真实的实验样品。我们的方法是数值，使我们能够访问完整的邻近效应制度。在第一部分中，我们研究了具有非平凡磁织构的非均匀铁磁体中的超导邻近效应和由此产生的局域态密度。我们在第一部分中的两个主要结果是布洛赫和内尔畴壁如何影响邻近诱导的超导关联的研究和研究的超导邻近效应在锥形铁磁体。后一个主题应该是相关的铁磁体何，这是最近在实验中使用，以证明产生和维持长程三重态超导关联的可能性。在这项工作的第二部分中，我们调查的逆邻近效应，强调在超导区域的感应磁化强度的结果的“泄漏”的铁磁区域。结果表明，自旋-DIPS的存在下修改先前在文献中获得的结论，在超导区域的感应磁化。特别是，我们发现自旋DIPS可以触发磁化的反屏蔽效应，导致在超导区域与\textit{the same sign}在邻近铁磁体的感应磁化。
We theoretically study the local density of states in superconducting proximity structure where two superconducting terminals are attached to a side surface of a normal-metal wire. Using the quasiclassical Green's function method, the energy spectrum is obtained for both of spin-singlet $s$-wave and spin-triplet $p$-wave junctions. In both of the cases, the decay length of the proximity effect at the zero temperature is limited by a depairing effect due to inelastic scatterings. In addition to the depairing effect, in $p$-wave junctions, the decay length depends sensitively on the transparency…
We study the superconducting proximity effect in inhomogeneous systems in which a disordered or quasicrystalline normal-state wire is connected to a BCS superconductor. We self-consistently compute the local superconducting order parameters in the real space Bogoliubov-de Gennes framework for three cases, namely, when states are i) extended, ii) localized or iii) critical. The results show that the spatial decay of the superconducting order parameter as one moves away from the normal-superconductor interface is power law in cases i) and iii), stretched exponential in case ii). In the quasicrys…
The paradigmatic Mott insulator arises in strongly correlated systems, where strong local repulsion localizes interacting particles in underlying egg-holder-like potential. The corresponding Mott transition reflects delocalization of the charges either by varying parameters of the system and temperature, or by applied current, the latter being referred to as the dynamic Mott transition. Recently, the dynamic Mott transition was experimentally observed on the vortex system trapped by the periodic proximity array and described in terms of non-Hermitian theory of nonequilibrium processes. Here we…
High bias anomaly in YBa2Cu3O7/LaMnO_{3+delta}/YBa2Cu3O7 Superconductor/Ferromagnetic Insulator/Superconductor junctions: Evidence for a long-range superconducting proximity effect through the conduction band of a ferromagnetic insulator
研究了超导体/铁磁绝缘体/超导体（$_2$ O $_{7-x}$ /LaMnO $_{3+δ}$ /$_2$ O $_3$）隧道结的垂直输运特性.在一个大的偏置电压$V\sim 1$ V，我们观察到一个阶梯状的开始过电流，发生在超导转变温度$T<T_c$以下，很容易被磁场抑制。这种现象是由于非平衡电子通过Fowler-Nordheim隧穿过程注入到铁磁绝缘体导带中的一种新型的超导邻近效应。强非平衡布居的发生证实了在大偏压下的光子发射的检测。由于我们的铁磁绝缘体中的导带是强自旋极化的，所观察到的长程（20 nm）邻近效应为非传统的自旋三重态超导态提供了证据。
Coupling a conventional s-wave superconductor to a ferromagnet allows, via the proximity effect, to generate superconducting triplet correlations. This feature can be employed to achieve a superconducting triplet spin-valve effect in superconductor-ferromagnet (SF) hybrid structures, for example by switching the magnetizations of the ferromagnets between parallel and antiparallel configurations in F1SF2 and SF1F2 trilayers, or in SF bilayers with both Rashba and Dresselhaus SOC. It was recently reported that geometric curvature can control the generation of long ranged triplets. We use this pr…
We investigate the electron-phonon cooling power in disordered electronic systems with a special focus on mesoscopic superconducting proximity structures. Employing the quasiclassical Keldysh Green's function method, we obtain a general expression for the cooling power perturbative in the electron-phonon coupling, but valid for arbitrary electronic systems out of equilibrium. We apply our theory to several disordered electronic systems valid for an arbitrary relation between the thermal phonon wavelength and the electronic mean free path due to impurity scattering. Besides recovering the known…
Andreev reflection spectroscopy on Bi$_{2}$X$_{3}$ (X = Se, Te) topological insulators: Implications for the c-axis superconducting proximity effect
利用Andreev反射（AR）作为超导邻近效应（PE）的实验规范，我们评估了s波超导体与拓扑绝缘体Bi $_{2}$ X $_{3}$（X=Se，Te）之间的c轴PE所诱导的超导性的拓扑纯度.在4.2 K下用Nb针尖在Bi $_{2}$ X $_{3}$单晶上进行点接触AR光谱。扫描隧道光谱也被用来定位费米能级$E_F$相对于晶体中的狄拉克点。AR数据进行了分析与Blonder-Tinkham-Klapwijk理论，考虑到尖端诱导的自旋轨道耦合，费米表面失配，并在$E_F$的体带和拓扑表面状态的共存。我们的研究结果表明，可以接近诱导到Bi $_{2}$ X $_{3}$的超导电性主要是非拓扑的。
Generalized quasiclassical theory of the long-range proximity effect and spontaneous currents in superconducting heterostructures with strong ferromagnets
We investigate inverse proximity effects in a spin-triplet superconductor (TSC) interfaced with a ferromagnet (FM), assuming different types of magnetic profiles and chiral or helical pairings. The region of the coexistence of spin-triplet superconductivity and magnetism is significantly influenced by the orientation and spatial extension of the magnetization with respect to the spin configuration of the Cooper pairs, resulting into clearcut anisotropy signatures. A characteristic mark of the inverse proximity effect arises in the induced spin-polarization at the TSC interface. This is unexpec…
Triplet proximity effect in superconducting heterostructures with a half-metallic layer
本文提出了描述半金属层异质结构中超导邻近效应的Usadel理论。结果表明，半金属内部的全自旋极化引起了超导体（S）-铁磁体（F）-半金属（HM）三层中的巨三重态自旋阀效应，以及S/F/HM/F/S系统中的$φ_0$结的形成.此外，我们考虑了原子厚度的S/F/HM三层膜的精确可解模型，并证明了它再现了Usadel方法中发现的自旋阀效应的主要特征。我们的结果与最近关于${\rm MoGe/Cu/Ni/CrO_2}$杂化材料中自旋阀效应的实验数据定性一致[A. Singh等人，Rev. X 5，021019（2015）]。
Proximity-effect-induced Superconducting Gap in Topological Surface States - A Point Contact Spectroscopy Study of NbSe2/Bi2Se3 Superconductor-Topological Insulator Heterostructures
