1,160 research outputs found

    Microscopic Analysis of Low-Frequency Flux Noise in YBa2_2Cu3_3O7_7 Direct Current Superconducting Quantum Interference Devices

    Full text link
    We use low-temperature scanning electron microscopy combined with SQUID detection of magnetic flux to image vortices and to investigate low-frequency flux noise in YBa2_2Cu3_3O7_7 thin film SQUIDs. The low-frequency flux noise shows a nonlinear increase with magnetic cooling field up to 60 μ\muT. This effect is explained by the surface potential barrier at the SQUID hole. By correlating flux noise data with the spatial distribution of vortices, we obtain information on spatial fluctuations of vortices on a microscopic scale, e.g. an average vortex hopping length of approximately 10 nm.Comment: submitted to Applied Physics Letter

    3-junction SQUID rocking ratchet

    Full text link
    We investigate 3-junction SQUIDs which show voltage rectification if biased with an ac current drive with zero mean value. The Josephson phase across the SQUID experiences an effective ratchet potential, and the device acts as an efficient rocking ratchet, as demonstrated experimentally for adiabatic and nonadiabatic drive frequencies. For high-frequency drives the rectified voltage is quantized due to synchronization of the phase dynamics with the external drive. The experimental data are in excellent agreement with numerical simulations including thermal fluctuations.Comment: 5 pages, 4 figures -- Fig.4 revise

    Imaging of Thermal Domains in ultrathin NbN films for Hot Electron Bolometers

    Full text link
    We present low-temperature scanning electron microscopy (LTSEM) investigations of superconducting microbridges made from ultrathin NbN films as used for hot electron bolometers. LTSEM probes the thermal structure within the microbridges under various dc current bias conditions, either via electron-beam-induced generation of an unstable hotspot, or via the beam-induced growth of a stable hotspot. Such measurements reveal inhomogeneities on a micron scale, which may be due to spatial variations in the NbN film or film-interface properties. Comparison with model calculations for the stable hotspot regime confirm the basic features of common hot spot models.Comment: 3 pages, 3 figure
    • …
    corecore