Mixing of topological states with superconductivity could result in topological superconductivity with the elusive Majorana fermions potentially applicable in fault-tolerant quantum computing. One possible candidate considered for realization of topological superconductivity is thin bismuth films on Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212). Here, we present angle-resolved and core-level photoemission spectroscopy studies of thin Bi films grown {\it in-situ} on as-grown Bi2212 that show the absence of proximity effect. We find that the electron transfer from the film to the substrate and the resulting severe underdoping of Bi2212 at the interface is a likely origin for the absence of proximity effect. We also propose a possible way of preventing a total loss of proximity effect in this system. Our results offer a better and more universal understanding of the film/cuprate interface and resolve many issues related to the proximity effect.
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…
We investigate the proximity effect in a heterostructure of the topological insulator (TI) \BiSe\ deposited on the HTSC material BSCCO. The latter is described by the one-band Hubbard model and is treated with cluster dynamical mean field theory (CDMFT), the TI layers being included via the CDMFT self-consistency loop. The penetration of superconductivity into the TI depends on the position of the Fermi level with respect to the TI gap. We illustrate the back action of the TI layer on the HTSC layer, in particular the gradual disappearance of Mott physics with increasing tunneling amplitude.
We theoretically study the proximity effect and the inverse proximity effect in a topological insulator/iron-based superconductor heterostructure based on the microscopic model. The superconducting order parameter is self-consistently calculated. Its magnitude decreases when the coupling of these two systems increases. The induced pairing order parameter exhibits negative and positive values, while the negative pairing near the $Γ=(0,0)$ point is dominant. This parameter has twofold symmetry and includes an $s$-wave component and a $d$-wave component. The magnitude of the induced pairing order…
We have investigated the structural, magnetic and superconducting properties of [Nb(1.5nm)/Fe(x)]$_{10}$ superlattices deposited on a thick Nb(50nm) layer. Our investigation showed that the Nb(50nm) layer grows epitaxially at 800$^\circ$C on Al$_2$O$_3$(1$\bar{1}$02) substrate. Samples grown at this condition posses a high residual resistivity ratio of 15-20. By using neutron reflectometry we show that Fe/Nb superlattices with $x<$ 4 nm form a depth-modulated FeNb alloy with concentration of iron varying between 60% and 90%. This alloy has properties of a weak ferromagnet. Proximity of this we…
Andreev Reflection without Fermi surface alignment in High T$_{c}$-Topological heterostructures
讨论了拓扑材料与高温$_{c}$超导体之间的邻近效应问题。在Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+δ}$和具有不同费米表面的材料（Bi $_{2}$ Te $_{3}$ \&石墨）之间产生结。这两种情况下揭示隧道光谱与Andreev反射一致。这通过磁场证实，磁场通过多普勒效应改变特征。这是一个单一的参数，占隧道进入屏蔽超电流建模。因此，隧穿涉及穿过异质结构的库珀对，这表明费米表面失配并不妨碍形成透明界面的能力，这是由扩展的布里渊区和不同的晶格对称性引起的。
We analyse the possibility of the appearance of spontaneous currents in proximated superconducting/normal metal (S/N) heterostructure when Cooper pairs penetrate into the normal metal from the superconductor. In particular, we calculate the free energy of the S/N structure. We show that whereas the free energy of the N film $F_{N}$ in the presence of the proximity effect increases compared to the normal state, the total free energy, which includes the boundary term $F_{B}$, decreases. The condensate current decreases $F_{N}$, but increases the total free energy making the current-carrying stat…
The effect of proximity of the magnetism of the Pr-based manganite (Pr0.6Sr0.4MnO3) on the superconductivity of Bi-based high-temperature superconductor (Bi1.75Pb0.25Sr2Ca2Cu3O10+d) was studied based on the results obtained from the magnetotransport and magnetization measurements. Decrease in the values of the upper critical field (HC2(0)) and an increase in the width of the superconducting transition (Delta TC) of Bi1.75Pb0.25Sr2Ca2Cu3O10+d were observed in proximity with the manganite. The combined effect of magnetic exchange interaction arising from the manganite, the leakage of Cooper-pair…
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）
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）]。
Motivated by the recent findings of unconventional superconductivity in $\mathrm{CoSi_2 / TiSi_2}$ heterostructures, we study the effect of interface induced Rashba spin orbit coupling on the conductance of a three terminal "T" shape superconducting device. We calculate the differential conductance for this device within the quasi-classical formalism that includes the mixing of triplet-singlet pairing due to the Rashba spin orbit coupling. We discuss our result in the light of the conductance spectra reported by Chiu {\it et al.} for $\mathrm{CoSi_2 / TiSi_2}$ heterostructures.
Generalized quasiclassical theory of the long-range proximity effect and spontaneous currents in superconducting heterostructures with strong ferromagnets
High-temperature superconductors (HTS) are important for potential applications and for understanding the origin of strong correlations. Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO), a van der Waals material, offers a platform to probe the physics down to a unit-cell. Guiding the flow of electrons by patterning 2DEGS and oxide heterostructures has brought new functionality and access to new science. Similarly, modifying superconductivity in HTS locally, on a small length scale, will be of immense interest for superconducting electronics. Here we report transport studies on few unit-cell thick BSCCO a…
Interfacial roughness and proximity effects in superconductor/ferromagnet CuNi/Nb heterostructures
本文报道了用磁控溅射法制备的Nb/Cu $_{60}$ Ni $_{40}$混合超导/铁磁体（S/F）双层膜的结构和电子性质。X射线和中子反射测量表明，沉积在Al $_2$ O $_3$（1 $\bar{1}$ 02）衬底上的异质结构的总界面粗糙度和不同界面粗糙度的垂直相关性都低于沉积在Si（111）衬底上的异质结构。互感实验研究了界面粗糙度对超导转变温度$T_C$的影响。这些测量结果表明，沉积在Al $_2$ O $_3$上的异质结构中的$\sim$比沉积在Si上的异质结构高$T_C$ 4%。我们将这种效应归因于S层中电子的更高平均自由程，这是由界面处的扩散散射的抑制引起的。然而，$T_C$对铁磁层厚度的依赖性在两个系统中没有显著差异，表明库珀对的透明性上的界面粗糙度的微弱影响。
Unconventional superconductors have been long sought for their potential applications in quantum technologies and devices. A key challenge impeding this effort is the difficulty associated with probing and characterizing candidate materials and establishing their order parameter. In this Letter, we present a platform that allows us to spectroscopically probe unconventional superconductivity in thin-layer materials via the proximity effect. We show that inducing an s-wave gap in a sample with an intrinsic d-wave instability leads to the formation of bound-states of quasiparticle pairs, which ma…
Two-dimensional topological superconducting phases emerged from d-wave superconductors in proximity to antiferromagnets
基于最近在Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+δ}$衬底上生长的单层CuO $_{2}$中的无结超导电性的观察，我们研究了在反铁磁（AF）绝缘体附近的二维$t$ - $J$模型所描述的二维超导相.我们发现：（1）邻近感应AF场可以驱动节d波SC态通过连续跃迁进入无节d波配对态。(ii)在强场区中，能量有利的配对态具有扩展的s波对称性，可以是节态或无节态。(iii)在纯d波和s波配对相位之间，出现两个拓扑上不同的SC相位，具有（$s+$ i $d$）对称性，即，弱配对相和强配对相，发现弱配对相是受谷对称性保护的$Z_{2}$拓扑超导体，表现出强的无带隙非手征边缘模.这些结果有力地表明，高$T_{c}$超导体在反铁磁体附近可以实现完全能隙对称性保护的拓扑超导。
The AC conduction of epitaxially-grown SmB$_6$ thin films and superconducting heterostructures of SmB$_6$/YB$_6$ are investigated via time domain terahertz spectroscopy. A two-channel model of thickness-dependent bulk states and thickness-independent surface states accurately describes the measured conductance of bare SmB$_6$ thin films, demonstrating the presence of surface states in SmB$_6$. While the observed reductions in the simultaneously-measured superconducting gap, transition temperature, and superfluid density of SmB$_6$/YB$_6$ heterostructures relative to bare YB$_6$ indicate the pe…
Proximity and Josephson effects in superconductor - antiferromagnetic Nb / γ-Fe50Mn50 heterostructures
我们研究了超导反铁磁双层膜中的邻近效应，并报道了第一个三层S/AF/S约瑟夫森结的制备和测量。无序的f.c.c.采用γ-Fe50Mn50合金作为AF，S为Nb。测量微米和亚微米尺度的结，并且$J_C (d_AF)$的缩放在AF中给出2.4 nm的相干长度，其与由于双层样品中$T_C$的抑制而导致的相干长度相关。FeMn的扩散常数为1.7 \times 10 $^{-4}$ m $^2$ s $^-1$，并得到了费米能级的态密度。交换偏置FeMn/Co双层证实了在该厚度范围内FeMn的AF性质。
Possible Nodeless Superconducting Gaps in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ and YBa$_2$Cu$_3$O$_{7-x}$ Revealed by Cross-Sectional Scanning Tunneling Spectroscopy
铜氧化物高温超导体中的配对及其起源仍然是凝聚态物理学中最持久的谜团之一。利用截面扫描隧道显微镜/光谱，我们清楚地揭示了BiPDMATHABMM Sr $_2$ CaCu $_2$ O $_{8+δ}$（Bi 2212）和YBaPDMATHABMM Cu $_3$ O $_{7-x}$（YBCO）超导能隙结构沿其$c$ -轴的空间依赖性或不均匀性，其尺度小于层间距.通过对Bi 2212单晶和YBCO薄膜的（100）面隧穿，我们在每个样品的不同区域都观察到了具有扩展的平坦零电导底部的U形隧穿谱和V形带隙结构。在YBCO薄膜上，隧穿到（110）面的带隙为U形，没有零偏压峰。我们的分析表明，U形间隙可能是一个无节点的超导间隙。V形间隙具有非常小的幅度，并且可能是由具有较大U形间隙的区域引起的接近。
Strong variations in superconducting critical temperatures in different families of the cuprate perovskites, even with similar hole doping in their copper-oxygen planes, suggest the importance of lattice modulation effects. The one-dimensional incommensurate lattice modulation (ILM) of Bi_2Sr_2CaCu_2O_{8+y}, with the average atomic positions perturbed beyond the unit cell, offers an ideal test ground for studying the interplay between superconductivity and the long-range incommensurate lattice fluctuations. Here we report Scanning nano X-ray Diffraction (SnXRD) imaging of incommensurate lattic…
Proximity effect induced intriguing superconductivity in van der Waals heterostructure of magnetic topological insulator and conventional superconductor
We introduce a two-dimensional Chern insulator in proximity to a $d$-wave pseudogap state of the high-T$_c$ superconducting material as an effective platform to realize the higher order topological system. The proximity-induced $d$-density-wave (DDW) order in the Chern insulator layer serves as an effective mass. The edge states will be fully gapped by this DDW order. In the real space, the sign of the DDW order parameter changes at the system corners due to the $d$-wave factor, leading to the gapless corner states, indicating that this system may be in a higher order topological state. The hi…
Superconductor-topological insulator (SC-TI) heterostructures were proposed to be a possible platform to realize and control Majorana zero-modes. Despite experimental signatures indicating their existence, univocal interpretation of the observed features demands theories including realistic electronic structures. To achieve this, we solve the Kohn-Sham-Dirac-Bogoliubov-de Gennes equations for ultrathin Bi$_2$Se$_3$ films on superconductor PdTe, within the fully relativistic Korringa-Kohn-Rostoker method, and investigate quasiparticle spectra as a function of chemical potential and film thickne…
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…
