A hybrid system which consists of a superconducting (SC) Pb film (100 nm thickness) containing $\sim$1 vol% single domain ferromagnetic (FM) Co particles of mean-size $\sim$4.5 nm reveal unusual magnetic properties: (i) a controlled switching between the usual diamagnetic and the unusual paramagnetic Meissner effect in field cooling as well as in zero-field cooling experiments (ii) amplification of the positive magnetization when the sample enters the SC state below T$_c$. These experimental findings can be explained by the formation of spontaneous vortices and the possible alignment of these vortices due to the foregoing alignment of the Co particle FM moments by an external magnetic field.
The Meissner effect is one of the defining properties of superconductivity, with a conventional superconductor completely repelling an external magnetic field. In contrast to this diamagnetic behavior, odd-frequency superconducting pairing has often been seen to produce a paramagnetic Meissner effect, which instead makes the superconductor unstable due to the attraction of magnetic field. In this work we study how both even- and odd-frequency superconducting pairing contributes to the Meissner effect in a generic two-orbital superconductor with a tunable odd-frequency pairing component. By div…
Boundary surfaces of nodal gap superconductors can host Andreev bound states (ABS) which develop a paramagnetic response under external RF field in contrast to the bulk diamagnetic response of the bulk superconductor. At low temperature this surface paramagnetic response dominates and enhances the nonlinear RF response of the sample. With a recently developed photoresponse imaging technique, the anisotropy of this "paramagnetic" nonlinear Meissner response, and its current direction (angular) and RF power dependence has been systematically studied. A theoretical model describing the current fl…
In 1933, Meissner and Ochsenfeld reported the expulsion of magnetic flux, the diamagnetic Meissner effect, from the interior of superconducting lead. This discovery was crucial in formulating the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity. In exotic superconducting systems BCS theory does not strictly apply. A classical example is a superconductor-magnet hybrid system where magnetic ordering breaks time-reversal symmetry of the superconducting condensate and results in the stabilisation of an odd-frequency superconducting state. It has been predicted that under appropriate con…
Doped Bi$_2$Se$_3$ is proposed to be a nematic superconductor originating from unusual inter-orbital pairing. We classify all induced superconducting pair correlations in Bi$_2$Se$_3$ and discover that intra-orbital odd-frequency pairing dominates over a significant range of frequencies. Moreover, we explore the contributions of even- and odd-frequency pairing to the Meissner effect, including separating intra- and inter-band processes in the response function. Contrary to expectations, and due to inter-band contributions, we find a diamagnetic odd-frequency Meissner effect.
An increase of the magnetic moment in superconductor/ferromagnet (S/F) bilayers V(40nm)/F [F$=$Fe(1,3nm), Co(3nm), Ni(3nm)] was observed using SQUID magnetometry upon cooling below the superconducting transition temperature Tc in magnetic fields of 10 Oe to 50 Oe applied parallel to the sample surface. A similar increase, often called the paramagnetic Meissner effect (PME), was observed before in various superconductors and superconductor/ferromagnet systems. To explain the PME effect in the presented S/F bilayers a model based on a row of vortices located at the S/F interface is proposed. Acc…
Magnetic force microscopy measurement of the penetration depth in superconductors from Meissner repulsion
本文报道了一种利用磁力显微镜（MFM）检测超导体抗磁响应，局部测量超导体穿透深度$λ$的方法。我们提取$λ$通过拟合的高度依赖性的悬浮力在迈斯纳状态下使用的分析模型，近似的MFM尖端作为一个单域，截头圆锥壳。我们证明了两个$_2$铜$_3$ O $_{6+x}$单晶与两个MFM尖，所获得的值与以前的结果吻合得很好。这种方法不受尖端宽度的影响，并且可以应用于类似但不相同的尖端。
Conventional superconductors respond to external magnetic fields by generating diamagnetic screening currents. However, theoretical work has shown that one can engineer systems where the screening current is paramagnetic, causing them to attract magnetic flux -- a prediction that has recently been experimentally verified. In contrast to previous studies, we show that this effect can be realized in simple superconductor/normal-metal structures with no special properties, using only a simple voltage bias to drive the system out of equilibrium. This is of fundamental interest, since it opens up a…
Recently, interest in Superconductor (S)-Normal (N) interfaces was renewed by the observation of exotic proximity effects in various systems, including S/semiconductor, S/ferromagnet, and S/topological insulator. In general, the proximity effect is enhanced in transparent weak links where coherent Andreev reflection is possible. Also, it is a common knowledge that the proximity effect is, by definition, is a localized phenomenon that can only be active in each S/N interface region. However, here we show that a three-dimensional (3D) macroscale proximity effect is realized in few-micrometer-thi…
The coupling of a superconductor to a different material often results in a system with unconventional superconducting properties. A conventional superconductor is a perfect diamagnet expelling magnetic fields out of its volume, a phenomenon known as Meissner effect. Here, we show that the simple adsorption of a monolayer of chiral molecules, which are non-magnetic in solution, onto the surface of a conventional superconductor can markedly change its diamagnetic Meissner response. By measuring the internal magnetic field profile in superconducting Nb thin films under an applied transverse fiel…
The mechanism of the interplay between superconductivity and magnetism is one of the intriguing and challenging problems in physics. Theory has predicted that the ferromagnetic order can coexist with the superconducting order in the form of a spontaneous vortex phase in which magnetic vortices nucleate in the absence of an external field. However, there has been no rigorous demonstration of spontaneous vortices by bulk magnetic measurements. Here we show the results of experimental observations of spontaneous vortices using a superconductor/ferromagnet fractal nanocomposite, in which supercond…
Anomalous local magnetic field distribution and strong pinning in CaFe1.94Co0.06As2 single crystals
CaFe1.94Co0.06As2单晶的磁光成像显示超导体的迈斯纳区域内的异常剩余磁化。非常规的形状的局部磁化磁滞回线表明混合物的超导和磁性分数控制的响应。在超导转变温度附近，局部磁场超过所施加的磁场，导致抗磁性到正磁化转变。在局部磁场分布中观察到的异常伴随着在CaFe 1.94 Co 0.06 As 2单晶中增强的体钉扎。我们提出我们的结果表明超导性和磁关联共存。
Probing the Meissner effect in single crystals of $\mathbf{Bi_2Sr_2Ca_2Cu_3O_{10+δ}}$ via wide-field quantum microscopy under high pressure
School of Engineering, Institute of Science Tokyo（东京科学大学工学院）；Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science（物质材料研究机构纳米结构研究中心）；Department of Mechanical and Electrical Systems Engineering, Kyoto University of Advanced Science (KUAS)（京都先端科学大学机电系统工程学院）；National Institutes for Quantum Science and Technology (QST)（量子科学技术研究开发机构）
Supercurrent effect in a charge density wave intertwined superconductor
School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology（华中科技大学物理学院、武汉国家强磁场中心）；Department of Physics, Zhejiang University（浙江大学物理系）；Hefei National Laboratory（合肥国家实验室）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Department of Physics, Southern University of Science and Technology（南方科技大学物理系）；Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong)（粤港澳大湾区量子科学中心（广东））
