Search results for "superconductor"
showing 10 items of 93 documents
Spin Hanle effect in mesoscopic superconductors
2014
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).
Microwave Response of Ceramic MgB2 Samples
2009
The microwave response of ceramic MgB2 has been investigated as a function of temperature and external magnetic field by two different techniques: microwave surface impedance and second-harmonic emission measurements. The measurements of the surface resistance have shown that microwave losses in MgB2 are strongly affected by the magnetic field in the whole range of temperatures below Tc, even for relatively low field values. The results have been accounted for in the framework of the Coffey and Clem model hypothesizing that in different temperature ranges the microwave current induces fluxons to move in different regimes. In particular, the results at temperatures close to Tc have been quan…
Normal metal - insulator - superconductor thermometers and coolers with titanium-gold bilayer as the normal metal
2018
We have fabricated superconductor - insulator - normal metal - insulator - superconductor (SINIS) tunnel junctions in which Al acts as the superconductor, AlOx is the insulator, and the normal metal consists of a thin Ti layer (5 nm) covered with a thicker Au layer (40 nm). We have characterized the junctions by measuring their current-voltage curves between 60 mK and 750 mK. For comparison, the same measurements have been performed for a SINIS junction pair whose normal metal is Cu. The Ti-Au bilayer decreases the SINIS tunneling resistance by an order of magnitude compared to junctions where Cu is used as normal metal, made with the same oxidation parameters. The Ti-Au devices are much mo…
Tunneling junctions of the heavy-fermion superconductor UPd2Al3
1998
Abstract Tunneling spectroscopy on planar Giaever-type junctions is a powerful tool for the investigation of the superconducting state of metals. Since it is possible to prepare high-quality epitaxial thin films of the heavy-fermion compound UPd 2 Al 3 , this method can be used to examine the energy gap of this presumably unconventional superconductor. We prepared cross-junctions consisting of a UPd 2 Al 3 base electrode and a metal counter electrode (Au, Al or Ag). These small area contacts without artificial barriers have only low junction resistances and suffer from irreproducibility. On the other hand, on some of those junctions we observed BCS-like tunneling conductivity. In order to i…
Very large thermophase in ferromagnetic josephson junctions
2014
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).
Magnetic field-controlled 0−π transitions and their experimental signatures in superconductor-ferromagnet-superconductor junctions
2019
Superconductor-ferromagnet-superconductor Josephson junctions are known to exist in the $0$ and $\pi$ states with the transitions between them controlled by the temperature and ferromagnetic interlayer thickness. We demonstrate that these transitions can be controlled also by the external magnetic field directed perpendicular to the layers. By varying the ratio of diffusion coefficients in superconducting and ferromagnetic layers, these field-controlled transitions can be made detectable for arbitrary large value of the exchange energy in the ferromagnet. We also show that the $0$-$\pi$ transitions in the perpendicular field can be observed as the specific features of the flux-flow conducti…
Anomalous current in diffusive ferromagnetic Josephson junctions
2017
We demonstrate that in diffusive superconductor/ferromagnet/superconductor (S/F/S) junctions a finite, anomalous Josephson current can flow even at zero phase difference between the S electrodes. The conditions for the observation of this effect are noncoplanar magnetization distribution and a broken magnetization inversion symmetry of the superconducting current. The latter symmetry is intrinsic for the widely used quasiclassical approximation and prevented previous works based on this approximation from obtaining the Josephson anomalous current. We show that this symmetry can be removed by introducing spin-dependent boundary conditions for the quasiclassical equations at the superconducti…
Electromagnetic response of LaO_0.94F_0.06FeAs: AC susceptibility and microwave surface resistance
2009
We discuss on the electromagnetic response of a polycrystalline sample of LaO_0.94F_0.06FeAs exposed to DC magnetic fields up to 10 kOe. The low- and high-frequency responses have been investigated by measuring the AC susceptibility at 100 kHz and the microwave surface resistance at 9.6 GHz. At low as well as high DC magnetic fields, the susceptibility strongly depends on the amplitude of the AC driving field, highlighting enhanced nonlinear effects. The field dependence of the AC susceptibility exhibits a magnetic hysteresis that can be justified considering the intragrain-field-penetration effects on the intergrain critical current density. The microwave surface resistance exhibits a cloc…
Slow magnetic fluctuations and superconductivity in fluorine-doped NdFeAsO
2015
Among the widely studied superconducting iron-pnictide compounds belonging to the Ln1111 family (with Ln a lanthanide), a systematic investigation of the crossover region between the superconducting and the antiferromagnetic phase for the Ln = Nd case has been missing. We fill this gap by focusing on the intermediate doping regime of NdFeAsO(1-x)F(x) by means of dc-magnetometry and muon-spin spectroscopy measurements. The long-range order we detect at low fluorine doping is replaced by short-range magnetic interactions at x = 0.08, where also superconductivity appears. In this case, longitudinal-field muon-spin spectroscopy experiments show clear evidence of slow magnetic fluctuations that …
Moir\'e-enabled topological superconductivity
2020
The search for artificial topological superconductivity has been limited by the stringent conditions required for its emergence. As exemplified by the recent discoveries of various correlated electronic states in twisted van der Waals materials, moir\'e patterns can act as a powerful knob to create artificial electronic structures. Here, we demonstrate that a moir\'e pattern between a van der Waals superconductor and a monolayer ferromagnet creates a periodic potential modulation that enables the realization of a topological superconducting state that would not be accessible in the absence of the moir\'e. The magnetic moir\'e pattern gives rise to Yu-Shiba-Rusinov minibands and periodic mod…