Abstract:We report on a fabrication method and electron-transport measurements for submicron Josephson junctions formed by Cu nanowires coupling to superconducting planar Nb electrodes. The Cu nanowires with a resistivity of ρCu≃1 μΩ cm at low temperatures consisting of single-crystalline segments have been obtained by templated electrodeposition using anodic aluminum oxide as a porous matrix. The current-voltage characteristics of the devices have been studied as a function of temperature and magnetic field. For all j… Show more
“…Nickel nanowires of 100–150 nm in diameter were obtained by templated electro-deposition into a porous anodic alumina 34,35 , extracted, washed, and dispersed in heptane (see Supplementary Materials). Individual NWs were bonded to Nb-electrodes for 4-probe transport measurements, following the steps comprising a seeding onto a marked Si/SiO 2 substrate, electron lithography, magnetron sputtering, and lift-off processes (see Supplementary Materials and 36 ). A set of samples was fabricated with different distances between inner (voltage) electrodes and with NWs of different diameters.…”
We examine the influence of superconductivity on the magneto-transport properties of a ferromagnetic Ni nanowire connected to Nb electrodes. We show experimentally and confirm theoretically that the Nb/Ni interface plays an essential role in the electron transport through the device. Just below the superconducting transition, a strong inverse proximity effect from the nanowire suppresses superconducting correlations at Nb/Ni interfaces, resulting in a conventional anisotropic magneto-resistive response. At lower temperatures however, the Nb electrodes operate as superconducting shunts. As the result, the magneto-resistance exhibits a strongly growing hysteretic behavior accompanied by a series of saw-like jumps. The latter are associated with the penetration/escape of individual Abrikosov vortices that influence non-equilibrium processes at the Nb/Ni interface. These effects should be taken into account when designing superconducting quantum nano-hybrids involving ferromagnetic nanowires.
“…Nickel nanowires of 100–150 nm in diameter were obtained by templated electro-deposition into a porous anodic alumina 34,35 , extracted, washed, and dispersed in heptane (see Supplementary Materials). Individual NWs were bonded to Nb-electrodes for 4-probe transport measurements, following the steps comprising a seeding onto a marked Si/SiO 2 substrate, electron lithography, magnetron sputtering, and lift-off processes (see Supplementary Materials and 36 ). A set of samples was fabricated with different distances between inner (voltage) electrodes and with NWs of different diameters.…”
We examine the influence of superconductivity on the magneto-transport properties of a ferromagnetic Ni nanowire connected to Nb electrodes. We show experimentally and confirm theoretically that the Nb/Ni interface plays an essential role in the electron transport through the device. Just below the superconducting transition, a strong inverse proximity effect from the nanowire suppresses superconducting correlations at Nb/Ni interfaces, resulting in a conventional anisotropic magneto-resistive response. At lower temperatures however, the Nb electrodes operate as superconducting shunts. As the result, the magneto-resistance exhibits a strongly growing hysteretic behavior accompanied by a series of saw-like jumps. The latter are associated with the penetration/escape of individual Abrikosov vortices that influence non-equilibrium processes at the Nb/Ni interface. These effects should be taken into account when designing superconducting quantum nano-hybrids involving ferromagnetic nanowires.
“…The outer superconducting Nb leads are employed to apply a direct current (I bias ) or/and an alternating current (I AC ), while the inner pair of contacts serve as voltage probes, as displayed in Figure 1i. [45,46] The electrical transport behavior of the TI-based nanodevices is investigated with the aid of a 3 He cryostat down to a temperature of 0.4 K. Figure 2a shows the temperature dependence of the differential resistance (dV/dI) measured in a four-terminal configuration using an AC current of 40 nA at zero magnetic field. The measurements reveal that the Nb electrodes have a transition between the superconducting and normal state at around T c,Nb ≈ 6.5 K. From the relation of the electron-phonon coupling strength 2Δ∕k B T c,Nb ≈ 3.9, with k B the Boltzmann constant and inserting T c,Nb we estimate a Nb energy gap Δ of 1.4 meV at T = 0.…”
Section: Crystalline Structure and Microstructure Analysismentioning
confidence: 99%
“…Unfortunately, the two-critical-current phenomenon, as found here, was not observed in the four-terminal configuration of Nb/Cu/Nb junctions, so no direct comparison with that kind of junction is possible. [46] In Figure 2f, the normalized critical currents I c1 ∕I c1 (0) is plotted as a function of temperature. We compared our results to theoretical models of superconductor/normal metal/superconductor (SNS) junctions.…”
Section: Temperature Dependence Of the Superconductivity In Nb/sb 2 Tmentioning
Nanohybrid superconducting junctions using antimony telluride (Sb 2 Te 3) topological insulator nanoribbons and Nb superconducting electrodes are fabricated using electron beam lithography and magnetron sputtering. The effects of bias current, temperature, and magnetic field on the transport properties of the junctions in a four-terminal measurement configuration are investigated. Two features are observed. First, the formation of a Josephson weak-link junction. The junction is formed by proximity-induced areas in the nanoribbon right underneath the inner Nb electrodes which are connected by the few tens of nanometers short Sb 2 Te 3 bridge. At 0.5 K a critical current of 0.15 µA is observed. The decrease of the supercurrent with temperature is explained in the framework of a diffusive junction. Furthermore, the Josephson supercurrent is found to decrease monotonously with the magnetic field indicating that the structure is in the small-junction limit. As a second feature, a transition is also observed in the differential resistance at larger bias currents and larger magnetic fields, which is attributed to the suppression of the proximity-induced superconductive state in the nanoribbon area underneath the Nb electrodes.
“…A combination of this theory with the results of the surface-sensitive STS experiment offers a complete microscopic picture of the spatial and spectral evolution of the proximity vortex cores in a diffusive metal. Among possible candidates for S/N bilayers we chose Nb/Cu, a system commonly used for SNS junctions 10 , 28 – 32 . Fig.…”
Vortices in quantum condensates exist owing to a macroscopic phase coherence. Here we show, both experimentally and theoretically, that a quantum vortex with a well-defined core can exist in a rather thick normal metal, proximized with a superconductor. Using scanning tunneling spectroscopy we reveal a proximity vortex lattice at the surface of 50 nm—thick Cu-layer deposited on Nb. We demonstrate that these vortices have regular round cores in the centers of which the proximity minigap vanishes. The cores are found to be significantly larger than the Abrikosov vortex cores in Nb, which is related to the effective coherence length in the proximity region. We develop a theoretical approach that provides a fully self-consistent picture of the evolution of the vortex with the distance from Cu/Nb interface, the interface impedance, applied magnetic field, and temperature. Our work opens a way for the accurate tuning of the superconducting properties of quantum hybrids.
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