In a recent work, signatures of a pair of Majorana bound states (MBS) were found in a new experimental platform formed by EuS islands deposited on top of a gold surface which was made superconducting through proximity coupling to a superconductor. In this work, we provide a theoretical understanding for how MBS can be formed in EuS/Au/superconductor heterostructures. We focus on the strip geometry where a narrow ferromagnetic strip is deposited on a planar structure. We first explicitly map out the topological phase diagram of the EuS/Au/superconductor heterostructure using the lattice Green's function method. Importantly, we find that the chemical potential step between the region with and without EuS covering is a crucial ingredient for the creation of MBS of this set-up. Next, we focus on the Bogoliugov quasi-particles that are bound to the region under the EuS by Andreev reflections from the surrounding superconductors. Moreover, we obtain the topological regimes analytically using the scattering matrix method. Notably, we confirm that the normal reflections induced by the chemical potential step are essential for creating finite topological regimes. Furthermore, the area of the topological regimes shows periodic oscillation as a function of chemical potential as well as the sample width.
Magnetic texture modulated superconductivity in superconductor/ferromagnet shells of semiconductor nanowires
Stanford University（斯坦福大学）；SLAC National Accelerator Laboratory（SLAC国家加速器实验室）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Universidad de Chile（智利大学）；Danish Fundamental Metrology（丹麦基础计量）；Universidad de Santiago de Chile（圣地亚哥德智利大学）
Electronic structure of Bi2Te3/FeTe heterostructure: implications for unconventional superconductivity
利用分子束外延技术在SrTiO_3衬底上制备了由拓扑绝缘体Bi_2 Te_3和铁硫属化物FeTe组成的异质结构，并对其进行了角分辨光电子能谱分析。这个系统最近被发现显示出超导性，尽管每个组成材料的非超导性质。当FeTe与Bi_2Te_3的两个五重层界面时，我们发现Bi_2Te_3的Dirac-cone表面态向更高的结合能移动，而来自FeTe的费米能级处的类孔带向更低的结合能移动。这表明，电子电荷转移发生从FeTe的Bi 2 Te 3通过界面。目前的结果指出空穴掺杂的FeTe界面的非常规超导电性的发生的重要性。
Unconventional superconductivity and in particular triplet superconductivity have been front and center of topological materials and quantum technology research. Here we report our observation of triplet superconductivity in nonmagnetic CoSi$_2$/TiSi$_2$ heterostructures on silicon. CoSi$_2$ undergoes a sharp superconducting transition at a critical temperature $T_c \approx$ 1.5 K, while TiSi$_2$ is a normal metal. We investigate conductance spectra of both two-terminal CoSi$_2$/TiSi$_2$ tunnel junctions and three-terminal T-shaped CoSi$_2$/TiSi$_2$ superconducting proximity structures. We rep…
We observe proximity-induced superconductivity in the \textit{in situ} prepared heterostructures constructed by topological insulator Bi$_{2}$Te$_{3}$ thin films and high-temperature cuprate superconductors Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$. The superconducting gap maximum is about 7.6 meV on the surface of Bi$_{2}$Te$_{3}$ thin films with a thickness of two quintuple layers, and the gap value decreases with an increase in the film thickness. Moreover, the quasiparticle interference data show a clear evidence of a twofold symmetric superconducting gap with gap minima along one pair of the pr…
Observation of Two-Dimensional Bulk Electronic States in a Superconducting Topological Insulator Heterostructure Cux(PbSe)5(Bi2Se3)6: Implications for Unconventional Superconductivity
我们对Cux（PbSe）5（Bi 2Se 3）6（CPSBS; x = 1.47）（一种由拓扑绝缘体异质结构衍生的超导体）进行了角分辨光电子能谱（ARPES），以阐明与可能的非常规超导电性发生相关的电子态。当Cu嵌入到母体化合物（PbSe）5（Bi 2Se 3）6中时，我们观察到由于电子掺杂导致的体导带的明显能量偏移。CPSBS的光子能量相关的ARPES测量表明，所观察到的体带形成一个圆柱形的类电子费米面的布里渊区中心。体电子态的二维性质表明奇宇称Eu配对或偶宇称d波配对的发生，这两者都可以在超导态中提供马约拉纳束缚态的平台。
The interplay between superconductivity and ferromagnetism in the superconductor/ferromagnet (SC/FM) heterostructures generates many interesting physical phenomena, including spin-triplet superconductivity, superconducting order parameter oscillation, and topological superconductivity. The unique physical properties make the SC/FM heterostructures as promising platforms for future superconducting spintronics and quantum computation applications. In this article, we review important research progress of SC/FM heterostructures from superconducting spintronics to quantum computation, and it is or…
Topological superconductivity in quasi-one-dimensional systems is a novel phase of matter with possible implications for quantum computation. Despite years of effort, a definitive signature of this phase in experiments is still debated. A major cause of this ambiguity is the side effects of applying a magnetic field: induced in-gap states, vortices, and alignment issues. Here we propose a planar semiconductor-superconductor heterostructure as a platform for realizing topological superconductivity without applying a magnetic field to the 2D electron gas hosting the topological state. Time-rever…
The designer approach has become a new paradigm in accessing novel quantum phases of matter. Moreover, the realization of exotic states such as topological insulators, superconductors and quantum spin liquids often poses challenging or even contradictory demands for any single material. For example, it is presently unclear if topological superconductivity, which has been suggested as a key ingredient for topological quantum computing, exists at all in any naturally occurring material . This problem can be circumvented by using designer heterostructures combining different materials, where the …
A topological insulator (TI) interfaced with an s-wave superconductor has been predicted to host an unusual form of superconductivity known as topological superconductivity (TSC). Molecular beam epitaxy (MBE) has been the primary approach in the scalable synthesis of the TI/superconductor heterostructures. Although the growth of epitaxial TI films on s-wave superconductors has been achieved, it remains an outstanding challenge for synthesizing atomically thin TI/superconductor heterostructures, which are critical for engineering the TSC phase. Here, we used MBE to grow Bi2Se3 films with the co…
Interface-Induced Superconductivity in Magnetic Topological Insulator-Iron Chalcogenide Heterostructures
The Pennsylvania State University（宾夕法尼亚州立大学）；Rutgers University（罗格斯大学）；University of Washington（华盛顿大学）；Chinese Academy of Sciences（中国科学院）；Materials Research Institute, The Pennsylvania State University（宾夕法尼亚州立大学材料研究所）；National High Magnetic Field Laboratory（国家高磁场实验室）；Paul Scherrer Institute（保罗谢尔研究所）；National Institute of Standards and Technology（美国国家标准与技术研究院）
Two-dimensional superconductivity at the interface of a Bi2Te3/FeTe heterostructure
纳米尺度异质结界面的超导性为研究二维超导的奇异物理提供了独特的机会。在拓扑绝缘体和铁硫族化合物之间的界面处实现超导性对于探索涉及这两类新材料的几个最近的理论预测具有高度吸引力。在这里，我们报告运输测量的Bi 2 Te 3/FeTe异质结通过范德华外延，这表明超导性在界面处诱导的Bi 2 Te 3外延层的厚度甚至下降到一个五层。通过Berezinsky-Kosterlitz-Alzheimer无相变的存在以及在接近超导转变温度时面内和面外上临界场的发散比，证实了所观察到的超导性的二维性质，其最高转变温度约为12 K.由于Bi_2Te_3的界面超导性和Dirac表面态的结合，本工作所研究的异质结构为实现Majorana费米子提供了一个新的平台。
Complex oxide heterointerfaces can host a rich of emergent phenomena, and epitaxial growth is usually at the heart of forming these interfaces. Recently, a strong crystalline-orientation-dependent two-dimensional superconductivity was discovered at interfaces between KTaO3 single-crystal substrates and films of other oxides. Unexpectedly, rare of these oxide films was epitaxially grown. Here, we report the existence of superconductivity in epitaxially grown LaVO3/KTaO3(111) heterostructures, with a superconducting transition temperature of ~0.5 K. Meanwhile, no superconductivity was detected i…
Van der Waals heterostructures have risen as a tunable platform to combine different electronic orders, due to the flexibility in stacking different materials with competing symmetry broken states. Among them, van der Waals ferromagnets such as CrI3 and superconductors as NbSe2 provide a natural platform to engineer novel phenomena at ferromagnet-superconductor interfaces. In particular, NbSe2 is well known for hosting strong spin-orbit coupling effects that influence the properties of the superconducting state. Here we put forward a ferromagnet/NbSe2/ferromagnet heterostructure where the inte…
Ferromagnetic insulators can induce a strong exchange field in an adjacent superconductor via the magnetic proximity effect. This manifests as spin-splitting of the BCS density of states of the superconductor, an important ingredient for numerous superconducting spintronics applications and the realization of Majorana fermions. A crucial parameter that determines the magnitude of the induced spin-splitting in FI/S bilayers is the thickness of the S layer $d$: In very thin samples, the superconductivity is suppressed by the strong magnetism. By contrast, in very thick samples, the spin splittin…
Bi2Te3/Fe1+yTe heterostructures are known to exhibit interfacial superconductivity between two non-superconducting materials: Fe1+yTe as the parent compound of Fe-based superconducting materials and the topological insulator Bi2Te3. Here, we present a top-down approach starting from two-dimensional (2D) heterostructures to fabricate one-dimensional (1D) Bi2Te3/Fe1+yTe nanowires or narrow nanoribbons. We demonstrate that the Bi2Te3/Fe1+yTe heterostructure remains intact in nanostructures of widths on the order of 100 nm and the interfacial superconductivity is preserved, as evidenced by electri…
Hybrid superconductor-semiconductor heterostructures are promising platforms for realizing topological superconductors and exploring Majorana bound states physics. Motivated by recent experimental progress, we theoretically study how magnetic insulators offer an alternative to the use of external magnetic fields for reaching the topological regime. We consider different setups, where: (1) the magnetic insulator induces an exchange field in the superconductor, which leads to a splitting in the semiconductor by proximity effect, and (2) the magnetic insulator acts as a spin-filter tunnel barrier…
The introduction of superconductivity to the Dirac surface states of a topological insulator leads to a topological superconductor, which may support topological quantum computing through Majorana zero modes. The development of a scalable material platform is key to the realization of topological quantum computing. Here we report on the growth and properties of high-quality (Bi,Sb)2Te3/graphene/gallium heterostructures. Our synthetic approach enables atomically sharp layers at both hetero-interfaces, which in turn promotes proximity-induced superconductivity that originates in the gallium film…
We study a two-dimensional heterostructure comprised of a monolayer of the magnetic insulator chromium triiodide (CrI$_3$) on a superconducting lead (Pb) substrate. Through first-principles computation and a tight-binding model, we demonstrate that charge transfer from the Pb substrate dopes the CrI$_3$ into an effective half-metal, allowing for the onset of a gapless topological superconductivity phase via the proximity effect. This phase, in which there exists a superconducting gap only in part of the Fermi surface, is shown to occur generically in 2D half-metal-superconductor heterostructur…
Studies on the origin of the interfacial superconductivity of Sb2Te3/Fe1+yTe heterostructures
Bi 2 Te 3/Fe 1 +yTe异质结界面超导电性（SC）是近年来发现的一种新型的捕获和控制Majorana费米子的平台，引起了人们的广泛关注。在这里，我们提出的另一个拓扑绝缘体（TI）/Fe 1 +yTe异质结构，Sb 2 Te 3/Fe 1 +yTe，这也享有界面二维SC的研究。输运测量的结果支持的Fe 1 +yTe层的过量Fe浓度的减少，不仅增加了其反铁磁（AFM）的波动，但也提高了该异质结构系统的SC的质量。另一方面，该异质结构的界面SC被发现具有比Bi 2 Te 3/Fe 1 +yTe异质结构更宽范围的TI层厚度依赖性，这被认为是由于Sb 2 Te 3的高得多的体电导率增强了其顶部和底部拓扑表面态（TSS）之间的间接耦合。我们的研究结果提供了证据之间的相互作用的AFM秩序，巡回携带的TSS和诱导界面SC的TI/Fe 1 +yTe异质结构系统。
Interfaces between transition-metal oxides are able to host two-dimensional electron gases (2DEGs) and exhibit exotic quantum phenomena. Here we report the observation of superconductivity below 230 mK for the heterostructure composed of SrNbO3 (SNO) and SrTiO3 (STO). Different from some other counterparts with two insulators, the metallic SNO provides a novel mechanism to form a quasi 2DEG by charge transfer from bulk towards interface under strain. The superconductivity, residing within the strained SNO layer near the interface, is contributed by an electron system with record-low carrier de…
Driven-dissipative superconductivity in moiré heterostructure without attraction
Joint Quantum Institute, University of Maryland（马里兰大学联合量子研究所）；ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology（巴塞罗那科技大学光子科学研究所）；Institute of Quantum Electronics, ETH Zürich（苏黎世联邦理工学院量子电子学研究所）；Institute for Theoretical Physics, University of Cologne（科隆大学理论物理研究所）
Prediction of new superconducting bilayers heterostructures using quantum confinement and proximity effects
Politecnico di Torino（都灵理工大学）；National Research Nuclear University MEPhI (Moscow Engineering Physics Institute)（国立核研究大学莫斯科工程物理学院）；University of Milan（米兰大学）；University of Göttingen（哥廷根大学）
There is intense controversy around the unconventional superconductivity in strontium ruthenate, where the various theoretical and experimental studies suggest diverse and mutually exclusive pairing symmetries. Currently, the investigation is solely focused on only one material, Sr2RuO4, and the field suffers from the lack of comparison targets. Here, employing a density functional theory based analysis, we show that the heterostructure composed of SrRuO3 and SrTiO3 is endowed with all the key characteristics of Sr2RuO4, and, in principle, can host superconductivity. Furthermore, we show that …
Proximity effect induced intriguing superconductivity in van der Waals heterostructure of magnetic topological insulator and conventional superconductor
Recently, the natural heterostructure of (PbSe)5(Bi2Se3)6 has been theoretically predicted and experimentally confirmed as a topological insulator. In this work, we induce superconductivity in (PbSe)5(Bi2Se3)6 by implementing high pressure. As increasing pressure up to 10 GPa, superconductivity with Tc ~ 4.6 K suddenly appears, followed by an abrupt decrease. Remarkably, upon further compression above 30 GPa, a new superconducting state arises, where pressure raises the Tc to an unsaturated 6.0 K within the limit of our research. Combining XRD and Raman spectroscopies, we suggest that the emer…
Higher Order Topology and Nodal Topological Superconductivity in Fe(Se,Te) Heterostructures
我们从理论上证明了单层FeTe $_{1-x}$ Se $_x$-超导量子自旋霍尔材料-与单层FeTe -双共线反铁磁体-的异质结构实现了更高阶的拓扑超导相，其特征在于钉扎到样品角落的紧急马约拉纳零模式。给出了该系统的最小有效模型，分析了高阶拓扑的来源，并对拓扑相图进行了充分的刻画。尽管传统的s波配对，我们发现相当令人惊讶的出现一个新的拓扑节点超导体的相图。其特点是边缘依赖的马约拉纳平坦带，拓扑节点相的反铁磁手征对称性的保护。我们还讨论了实验的可行性，估计现实的模型参数，和鲁棒性的马约拉纳角模式对磁无序。我们的工作为高阶拓扑和非阿贝尔马约拉纳物理提供了一个新的实验可行的高温平台。
Artificially engineered topological superconductivity has emerged as a viable route to create Majorana modes, exotic quasiparticles which have raised great expectations for storing and manipulating information in topological quantum computational schemes. The essential ingredients for their realization are spin non-degenerate metallic states proximitized to an s-wave superconductor. In this context, proximity-induced superconductivity in materials with a sizable spin-orbit coupling has been heavily investigated in recent years. Although there is convincing evidence that superconductivity may i…
