We study how non-helical spin textures at the boundary between a topological insulator (TI) and a superconductor (SC) affect the proximity-induced superconductivity of the TI interface state. We consider TIs coupled to both spin-singlet and spin-triplet SCs, and show that for the spin-triplet parent SCs the resulting order parameter induced onto the interface state sensitively depends on the symmetries which are broken at the TI-SC boundary. For chiral spin-triplet parent SCs, we find that nodal proximity-induced superconductivity emerges when there is broken twofold rotational symmetry which forces the spins of the non-helical topological states to tilt away from the interface plane. We furthermore show that the Andreev conductance of lateral heterostructures joining TI-vacuum and TI-SC interfaces yields experimental signatures of the reduced symmetries of the interface states.
Following our previous results, which provide evidence for the emergence of a chiral p-wave triplet-pairing component in superconducting Nb upon the adsorption of chiral molecules, we turned to investigate whether such an effect can take place in a proximal superconductor consisting of metal on superconductor bilayer. Note that in such proximity systems, correlated electron-hole (Andreev) pairs exist in the normal metal rather than genuine Cooper pairs. To that end, we used scanning tunneling spectroscopy (STS) on thin Au films grown in-situ on NbN (a conventional s-wave superconductor) before…
Despite much effort for over the two decades, the paring symmetry of a Sr$_2$RuO$_4$ superconductor has been still unclear. In this Rapid Communication, motivated by the recent rapid progress in fabrication techniques for Sr$_2$RuO$_4$ thin-films, we propose a promising strategy for identifying the spin-triplet superconductivity in the thin-film geometry by employing an antisymmetric spin-orbit coupling potential and a Zeeman potential due to an external magnetic field. We demonstrate that a spin-triplet superconducting thin-film undergoes a phase transition from a helical state to a chiral st…
Helical Majorana fermions in d_{x^2-y^2} + i d_{xy}-wave topological superconductivity of doped correlated quantum spin Hall insulators
利用重整化平均场论研究了锯齿形带状蜂窝晶格Kane-Mele模型的大Hubbard U极限。基态表现出时间反演对称性（TRS）破缺d + i d '波超导电性。在大自旋轨道耦合下，纯Kane-Mele模型中具有非平凡自旋Chern数的Z2相在TRS破缺态（称为自旋Chern相）中持续存在，并且在边缘处具有两对反向传播的螺旋Majorana模.随着自旋-轨道耦合的降低，系统经历了从自旋-陈到手征超导态的拓扑量子相变。我们的研究结果可能的相关性adatom掺杂的石墨烯和irridate化合物进行了讨论。
Recently the evidence of the helical magnetic structure modulated along $c$-axis with the period of four lattice parameters was obtained in easy $ab$ plane ferromagnetic superconductor EuRbFe$_4$As$_4$ [K. Iida et al., Phys. Rev. B 100, 014506 (2019)]. We argue that such structure may appear due to the presence of superconductivity. In spite of the very small value of the exchange field acting on the superconducting electrons in EuRbFe$_4$As$_4$, the exchange mechanism of interaction between superconductivity and ferromagnetism could dominate over the electromagnetic one and this circumstance …
Strain-Induced Helical Superconductivity and the Zero-Field Diode Effect
Institute for Theory of Condensed Matter, Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院凝聚态理论研究所）；Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院量子材料与技术研究所）
In this letter we report on proximity superconductivity induced in CdTe-HgTe core-shell nanowires, a quasi-one-dimensional heterostructure of the topological insulator HgTe. We demonstrate a Josephson supercurrent in our nanowires contacted with superconducting Al leads. The observation of a sizable $I_c R_n$ product, a positive excess current and multiple Andreev reflections up to fourth order further indicate a high interface quality of the junctions.
We propose a device based on a topological Josephson junction where the helical edge states of a two-dimensional topological insulator are in close proximity to two superconducting leads. The presence of a magnetic flux through the junction leads to a Doppler shift in the spectrum of Andreev bound states, and affects the quantum interference between proximized edge states. We inspect the emergent features, accessing the density of states through a tunnel-coupled metallic probe, thus realizing a Topological Superconducting Quantum Interference Proximity Transistor (TSQUIPT). We calculate the ex…
Using a prototype model for proximity induced superconductivity on a bilayer square lattice, we show that interlayer tunneling can drive change in topology of the Bogoliubov quasiparticle bands. Starting with topologically trivial superconductors, transitions to a non-trivial $p_x + {\rm i} p_y$ state and back to another trivial state are discovered. We characterize these phases in terms of edge-state spectra and Chern indices. We show that these transitions can also be controlled by experimentally viable control parameters, the bandwidth of the metallic layer and the gate potential. Insights …
In the following paper we investigate the critical temperature $T_c$ behavior in the two-dimensional S/TI (S denotes superconductor and TI - topological insulator) junction with a proximity induced in-plane helical magnetization in the TI surface. The calculations of $T_c$ are performed using the general self-consistent approach based on the Usadel equations in Matsubara Green's functions technique. We show that the presence of the helical magnetization leads to the nonmonotonic behavior of the critical temperature as a function of the topological insulator layer thickness.
Due to the non-trivial topological band structure in type-II Weyl semimetal Tungsten ditelluride (WTe2), unconventional properties may emerge in its superconducting phase. While realizing intrinsic superconductivity has been challenging in the type-II Weyl semimetal WTe2, proximity effect may open an avenue for the realization of superconductivity. Here, we report the observation of proximity-induced superconductivity with a long coherence length along c axis in WTe2 thin flakes based on a WTe2/NbSe2 van der Waals heterostructure. Interestingly, we also observe anomalous oscillations of the di…
Signature of proximity induced triplet superconductivity in junctions made of the doped topological insulator $\rm Bi_2Se_3$ and the s-wave superconductor NbN
Gapless helical superconductivity on the surface of a three-dimensional topological insulator
最近的角分辨光电子能谱实验在超导NbSe $_2$衬底上生长的三维拓扑绝缘体Bi $_2$ Se $_3$薄膜的螺旋表面态中观察到了邻近诱导的超导能隙。当拓扑绝缘体中掺杂磁性Mn杂质时，电子态密度中的超导相干峰被强烈抑制，这被解释为拓扑表面态中螺旋超导性的完全破坏。受这些实验的启发，我们探索了一种不同的可能性：无带隙螺旋超导，其中无带隙电子态密度与非零螺旋超导序参量共存。我们在Abrikosov-Gor'kov框架下研究了一个与随机磁性杂质耦合的超导狄拉克费米子模型，在系统的相图中发现了有限的无带隙螺旋超导区域，包括邻近诱导超导和内禀超导。对于后者，我们推导出由于磁散射的超导转变温度的普遍抑制率，并在狄拉克点的费米能级，量子临界吸引强度的普遍增加率。
Interest in the superconducting proximity effect has been reinvigorated recently by novel optoelectronic applications as well as by the possible emergence of the elusive Majorana fermion at the interface between topological insulators and superconductors. Here we produce high-temperature superconductivity in Bi2Se3 and Bi2Te3 via proximity to Bi2Sr2CaCu2O8+δ, in order to access increasing temperature and energy scales for this phenomenon. This was achieved by a new mechanical bonding technique we developed, enabling the fabrication of high-quality junctions between materials, unobtainable by c…
Hole gases in planar germanium can have high mobilities in combination with strong spin-orbit interaction and electrically tunable g-factors, and are therefore emerging as a promising platform for creating hybrid superconductor-semiconductor devices. A key challenge towards hybrid Ge-based quantum technologies is the design of high-quality interfaces and superconducting contacts that are robust against magnetic fields. In this work, by combining the assets of aluminum, which provides good contact to the Ge, and niobium, which has a significant superconducting gap, we demonstrate highly transpa…
Two-dimensional helical superconductivity and gapless superconducting edge modes in the 1T$^\prime$-WS$_2$/2H-WS$_2$ heterophase bilayer
University of California, Santa Barbara（加州大学圣塔芭芭拉分校）；Brookhaven National Laboratory（布鲁海文国家实验室）；Stony Brook University（石溪大学）；Flatiron Institute（平顿研究所）；University of Wisconsin-Madison（威斯康星大学麦迪逊分校）；University of Nevada, Reno（内华达大学里诺分校）
Long range proximity effect in La2/3Ca1/3MnO3 (LCMO)/(100)YBa2Cu3O7-delta (YBCO) ferromagnet/superconductor bilayers: Evidence for induced triplet superconductivity in the ferromagnet
Proximity effect induced intriguing superconductivity in van der Waals heterostructure of magnetic topological insulator and conventional superconductor
We study supercurrent and proximity vortices in a Josephson junction made of disordered surface states of a three-dimensional topological insulator with a proximity induced in-plane helical magnetization. In a regime where the rotation period of helical magnetization is larger than the junction width, we find supercurrent 0-π crossovers as a function of junction thickness, magnetization strength, and parameters inherent to the helical modulation and surface states. The supercurrent reversals are associated with proximity induced vortices, nucleated along the junction width, where the number of…
Proximity induced superconductivity within the insulating (Li$_{0.84}$Fe$_{0.16}$)OH layers in (Li$_{0.84}$Fe$_{0.16}$)OHFe$_{0.98}$Se
用μ子自旋转动方法研究了绝缘中间体（Li $_{0.84}$ Fe $_{0.16}$）OH层对（Li $_{0.84}$ Fe $_{0.16}$）OHFe $_{0.98}$ Se磁性和超导性质的影响.结果表明，在低于$\simeq 10$ K的温度下，它不仅增强了FeSe层间的耦合，而且由于靠近FeSe层，它本身也成为超导体。在（Li $_{0.84}$ Fe $_{0.16}$）OH层中的超导电性最可能是类超导的，并且能隙值取决于序参量对称性，不超过1-1.5 meV。
We investigate the superconductivity (SC) driven by correlation effects in electron-doped bilayer BiH near a type-II van Hove singularity (vHS). By functional renormalization group, we find triplet $p$-wave pairing prevails in the interaction parameter space, except for spin density wave (SDW) closer to the vHS or when the interaction is too strong. Because of the large atomic spin-orbital coupling (SOC), the $p$-wave pairing occurs between equal-spin electrons, and is chiral and two-fold degenerate. The chiral state supports in-gap edge states, even though the low energy bands in the SC state…
Thickness-Driven Superconductor-Insulator Transition in (Cu,C)-1234 and Proximity-Induced Superconductivity Recovery in (Cu,C)-1234/YBCO Heterostructure
Shanghai University（上海大学）；Shanghai Key Laboratory of High Temperature Superconductors（上海市高温超导重点实验室）
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 resu…
One-dimensional systems proximity-coupled to a superconductor can be driven into a topological superconducting phase by an external magnetic field. Here, we investigate the effect of vortices created by the magnetic field in a type-II superconductor providing the proximity effect. We identify different ways in which the topological protection of Majorana modes can be compromised and discuss strategies to circumvent these detrimental effects. Our findings are also relevant to topological phases of proximitized quantum Hall edge states.
We establish quasi-two-dimensional thin films of iron-based superconductors (FeSCs) as a new high-temperature platform for hosting intrinsic time-reversal-invariant helical topological superconductivity (TSC). Based on the combination of Dirac surface state and bulk extended $s$-wave pairing, our theory should be directly applicable to a large class of experimentally established FeSCs, opening a new TSC paradigm. In particular, an applied electric field serves as a "topological switch" for helical Majorana edge modes in FeSC thin films, allowing for an experimentally feasible design of gate-co…
Superconductivity emerges in $1T$-TiSe$_2$ when its charge density wave (CDW) order is suppressed by Cu intercalation or pressure. Since the CDW state is thought to be an excitonic insulator, an interesting question is whether the superconductivity is also mediated by the excitonic fluctuations. We investigated this question as to the nature of doping induced superconductivity in Cu$_x$TiSe$_2$ by asking if it is consistent with the phonon-mediated pairing. We employed the {\it ab initio} density functional theory and density functional perturbation theory to compute the electron-phonon coupli…
Materials with transition metals in triangular lattices are of great interest for their potential combination of strong correlation, exotic magnetism and electronic topology. Kagome nets are of particular importance since the discovery of geometrically frustrated magnetism and topological band structures in crystals like Herbertsmithite and Fe3Sn2, respectively. KV3Sb5 was discovered to be a layered topological metal with a Kagome net of vanadium. Here, we fabricated Josephson Junctions (JJ) of K1-xV3Sb5 and induced superconductivity over long junction lengths. Through magnetoresistance and cu…
