1,259 research outputs found
3-junction SQUID rocking ratchet
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
Microscopic Analysis of Low-Frequency Flux Noise in YBaCuO Direct Current Superconducting Quantum Interference Devices
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 YBaCuO thin film SQUIDs. The low-frequency flux noise
shows a nonlinear increase with magnetic cooling field up to 60 T. 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
Semifluxons in Superconductivity and Cold Atomic Gases
Josephson junctions and junction arrays are well studied devices in
superconductivity. With external magnetic fields one can modulate the phase in
a long junction and create traveling, solitonic waves of magnetic flux, called
fluxons. Today, it is also possible to device two different types of junctions:
depending on the sign of the critical current density, they are called 0- or
pi-junction. In turn, a 0-pi junction is formed by joining two of such
junctions. As a result, one obtains a pinned Josephson vortex of fractional
magnetic flux, at the 0-pi boundary. Here, we analyze this arrangement of
superconducting junctions in the context of an atomic bosonic quantum gas,
where two-state atoms in a double well trap are coupled in an analogous
fashion. There, an all-optical 0-pi Josephson junction is created by the phase
of a complex valued Rabi-frequency and we a derive a discrete four-mode model
for this situation, which qualitatively resembles a semifluxon.Comment: 15 pages (Latex), 6 color figures (eps
Imaging of Thermal Domains in ultrathin NbN films for Hot Electron Bolometers
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
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