We isolated flux disorder effects on the transport at the critical point of the quantum magnetic field tuned Superconductor to Insulator transition (BSIT). The experiments employed films patterned into geometrically disordered hexagonal arrays. Spatial variations in the flux per unit cell, which grow in a perpendicular magnetic field, constitute flux disorder. The growth of flux disorder with magnetic field limited the number of BSITs exhibited by a single film due to flux matching effects. The critical metallic resistance at successive BSITs grew with flux disorder contrary to predictions of its universality. These results open the door for controlled studies of disorder effects on the universality class of an ubiquitous quantum phase transition.
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。
This is a short note presenting a repeated experiment of the half-quantized transport signature given by Majorana chiral modes living in a heterostructure formed by an s-wave superconductor and a quantum-anomalous-Hall insulator.
Nature of the quantum insulator to superconductor and superconductor to normal state transitions in cuprate superconductors
本文用量子临界现象的标度理论详细分析了La $_{2-x}$ Sr $_{x}$ CuO $_{4}$，Y $_{0.8}$ Ca $_{0.2}$-123，Tl-1212和Tl-2201的各种超导性质。我们的结果包括：实验数据是完全符合的2D绝缘体到超导体（ISQ）的过渡在欠掺杂的限制。量子临界性质似乎是相当于那些肮脏的2D玻色子系统与长程库仑相互作用。与以前的证据一起，这种转变似乎是铜酸盐超导体的一般特征。3D超导体到正常态的量子跃迁（SNQ）被证明不那么独特。需要更多的实验数据来明确地解决这种转变的性质。
A zero-temperature magnetic-field-driven superconductor to insulator transition (SIT) in quasi-two-dimensional superconductors is expected to occur when the applied magnetic-field crosses a certain critical value. A fundamental question is whether this transition is due to the localization of Cooper pairs or due to the destruction of them. Here we address this question by studying the SIT in amorphous WSi. Transport measurements reveal the localization of Cooper pairs at a quantum critical field B_c^1 (Bose-insulator), with a product of the correlation length and dynamical exponents zv~4/3 nea…
We consider the interface between a Bardeen-Cooper-Schrieffer superconductor and non-superconducting band insulator. We show that under certain conditions, such interfaces can have an elevated superconducting critical temperature, without increasing the strength of the pairing interaction at the interface. We identify the regimes where the interface critical temperature exceeds the critical temperature associated with a superconductor-vacuum interface.
Current-Induced Superconductor-Insulator Transition in Granular High-T_c Superconductors
在这项工作中，我们报告了一个系统的研究电流对颗粒Y $_{1-x}$ Pr $_{x}$ Ba $_{2}$ Cu $_{3}$ O $_{7-δ}$样品的超导性能的影响，x接近临界Pr浓度以上的超导性消失。结果表明，在外加电流的驱动下，超导体-绝缘体发生了量子相变（SIT），电流诱导的SIT可以看作是磁场调谐的SIT的动力学对应物.
We investigate Josephson junctions among conventional superconducting wires, in the presence of externally applied Zeeman fields and supercurrents. We demonstrate that the critical Josephson current and the current-phase relation of the junction depends on the relative orientation of the applied Zeeman fields and supercurrents. The controllability of the Josephson current relies on the stabilization of conventional superconductivity in high magnetic fields, due to the restoration of the opposite momentum opposite spin projection resonance at the Fermi level. We assert that our results can lead…
Superconductor-Ferromagnet (SF) heterostructures are of interest due to numerous phenomena related to the spin-dependent interaction of Cooper pairs with the magnetization. Here we address the effects of a magnetic insulator on the density of states of a superconductor based on a recently developed boundary condition for strongly spin-dependent interfaces. We show that the boundary to a magnetic insulator has a similar effect like the presence of magnetic impurities. In particular we find that the impurity effects of strongly scattering localized spins leading to the formation of Shiba bands c…
The magnetic field driven superconductor to insulator transition in thin films was theoretically analyzed via a vortex-charge duality transformation applied to the Hamiltonian. Vortices condensation was conjectured as the underline physical mechanism of the insulating phase. Experimental evidence supported duality symmetry across the magnetic-field driven superconductor to insulator transition in amorphous Indium Oxide films. Counterintuitively, duality symmetry is broken at low temperatures where the insulating phase develops strongly non linear current-voltage characteristics. Here, we follo…
Magnetic-field tuned superconductor to insulator transition was observed in a novel hybrid system of granular superconducting indium, deposited on indium oxide thin film, which exhibits global superconductivity at low magnetic fields. We have used annealing to tune the coupling to lie just at the borderline where superconductivity in the underlying InOx is suppressed, which is also close to the metal-insulator transition of the InOx. The hybrid system exhibits a "giant" magnetoresistance above the H-SIT, with critical behavior that manifests the duality between Cooper pairs and vortices.
Weakly Pinned Bose Glass vs. Mott Insulator Phase in Superconductors
本文研究了在匹配场$B_Φ$附近辐照超导体中局域磁通线玻色玻璃相的性质。排斥涡的相互作用破坏了预测在$B=B_Φ$发生的莫特绝缘体相。对于穿透深度与平均缺陷距离$λ/ d \leq 1$的比率，莫特绝缘体奇异性的残余在磁化、体积模量和磁化弛豫中保持可见，因为B在$B_Φ$附近变化。对于$λ\geq d$，随后的弱钉扎玻色玻璃的特征在于软库仑能隙的钉扎能量分布。
We study the Josephson effect in spin-singlet superconductor/helical $p$-wave superconductor junctions with a ferromagnetic barrier using the quasiclassical Green function method. It is found that both $\sinϕ$-type and $\cosϕ$-type current-phase relations always exist, irrespective of the gap symmetries in superconductors. The indispensable condition for the $\sinϕ$-type and $\cosϕ$-type current is that the magnetization must have a component parallel to the crystallographic $a$ or $b$ axis, which is distinct from the case of $p$-wave superconductor described by a $\vect{d}$-vector with a unif…
We study numerically the superconductor to insulator transition in two-dimensional phase-glass (or chiral-glass) models with varying degree of disorder. These models describe the effects of gauge disorder in superconductors due to random negative Josephson-junction couplings, or $π$ junctions. Two different models are considered, with binary and Gaussian distribution of quenched disorder, having nonzero mean. Monte Carlo simulations in the path-integral representation are used to determine the phase diagram and critical exponents. In addition to the usual superconducting and insulating phases,…
We study the transport properties of a diffusive Josephson junction between two spin-split superconductors made of superconductor-ferromagnetic insulator bilayers (FIS) on top of a 3D topological insulator (TI). We derive the corresponding Usadel equation describing the quasiclassical Green's functions in these systems and first solve the equation analytically in the weak-proximity case. We demonstrate the appearance of an anomalous phase in the absence of an external magnetic field. We also explore non-reciprocal electronic transport. Specifically, we calculate the junction's diode efficiency…
The antiferromagnetic(AFM) insulator-superconductor transition has been always a center of interest in the underlying physics of unconventional superconductors. The quantum phase transition between Mott insulator with AFM and superconductor can be induced by doping charge carriers in high-Tc cuprate superconductors. For the best characterized organic superconductors of k-(BEDT-TTF)2X (X=anion), a first order transition between AFM insulator and superconductor can be tuned by applied external pressure or chemical pressure. Also, the superconducting state can be directly developed from AFM insul…
As platforms of Majorana modes, topological insulator (quantum anomalous Hall insulator)/superconductor (SC) heterostructures have attracted tremendous attention over the past decade. Here we substitute the topological insulator by its higher-order counterparts. Concretely, we consider second-order topological insulators (SOTIs) without time-reversal symmetry and investigate SOTI/SC heterostructures in both two and three dimensions. Remarkably, we find that such novel heterostructures provide natural realizations of second-order topological superconductors (SOTSCs) which host Majorana corner m…
We present a model of a strongly correlated system with a non-Fermi liquid high temperature phase. Its ground state undergoes an insulator to superconductor quantum phase transition (QPT) as a function of a pairing interaction strength. Both the insulator and the superconductor are originating from the same interaction mechanism. The resistivity in the insulating phase exhibits the activation behavior with the activation energy, which goes to zero at the QPT. This leads to a wide quantum critical regime with an algebraic temperature dependence of the resistivity. Upon raising the temperature i…
We report on transport properties of the topological insulator single crystal $Sb2Te3$ nanoflakes with thickness about from 7 to 50nm. A steep drop of resistance is appeared near $3K$ in the ultrathin $Sb2Te3$ nanoflakes, manifesting a superconducting transition.The magnetic field induced superconductor insulator transition of disordered 2D superconductor system is observed in the nanoflakes.The results show that the existence of certain optimum degree of disorder is a necessary condition for emergence of superconductivity.Temperature dependence of magneto-resistance shows a consecutive transf…
