2,628 research outputs found
Fluxon-semifluxon interaction in an annular long Josephson 0-pi-junction
We investigate theoretically the interaction between integer and half-integer
Josephson vortices (fluxons and semifluxons) in an annular Josephson junction.
Semifluxons usually appear at the 0--boundary where there is a
-discontinuity of the Josephson phase. We study the simplest, but the most
interesting case of one -discontinuity in a loop, which can be created
only artificially. We show that measuring the current-voltage characteristic
after injection of an integer fluxon, one can determine the polarity of a
semifluxon. Depending on the relative polarity of fluxon and semifluxon the
static configuration may be stable or unstable, but in the dynamic state both
configurations are stable. We also calculate the depinning current of
fluxons pinned by an arbitrary fractional vortex.Comment: 8pages, 6 figures, submitted to PR
Observation of Andreev bound states in YBaCuO/Au/Nb ramp-type Josephson junctions
We report on Josephson and quasiparticle tunneling in YBa2Cu3O7-x(YBCO)/Au/Nb
ramp junctions of several geometries. Macroscopically, tunneling occurs in the
ab-plane of YBCO either in the (100) and (010) direction, or in the (110)
direction. These junctions have a stable and macroscopically well defined
geometry. This allows systematic investigations of both quasiparticle and
Josephson tunneling over a wide range of temperature and magnetic field. With
Nb superconducting, its gap appears in the quasiparticle conductance spectra as
Nb coherence peaks and a dip at the center of a broadened zero-bias conductance
peak (ZBCP). As we increase the temperature or an applied magnetic field both
the Nb coherence peaks and the dip get suppressed and the ZBCP fully develops,
while states are conserved. With Nb in the normal state the ZBCP is observed up
to about 77 K and is almost unaffected by an increasing field up to 7 T. The
measurements are consistent with a convolution of density of states with
broadened Andreev bound states formed at the YBCO/Au/Nb junction interfaces.
Since junctions with different geometries are fabricated on the same substrate
under the same conditions one expects to extract reliable tunneling information
that is crystallographic direction sensitive. In high contrast to Josephson
tunneling, however, the quasiparticle conductance spectra are crystallographic
orientation insensitive: independent whether the tunneling occurs in the (100)
or (110) directions, a pronounced ZBCP is always observed, consistent with
microscopic roughness of the junction interfaces. Qualitatively, all these
particularities regarding quasiparticle spectra hold regardless whether the
YBCO thin film is twinned or untwinned.Comment: 13 pages, 10 figure
Laser microscopy of tunneling magnetoresistance in manganite grain-boundary junctions
Using low-temperature scanning laser microscopy we directly image electric
transport in a magnetoresistive element, a manganite thin film intersected by a
grain boundary (GB). Imaging at variable temperature allows reconstruction and
comparison of the local resistance vs temperature for both, the manganite film
and the GB. Imaging at low temperature also shows that the GB switches between
different resistive states due to the formation and growth of magnetic domains
along the GB. We observe different types of domain wall growth; in most cases a
domain wall nucleates at one edge of the bridge and then proceeds towards the
other edge.Comment: 5 pages, 4 figures; submitted to Phys. Rev. Let
Cold atoms near superconductors: Atomic spin coherence beyond the Johnson noise limit
We report on the measurement of atomic spin coherence near the surface of a
superconducting niobium wire. As compared to normal conducting metal surfaces,
the atomic spin coherence is maintained for time periods beyond the Johnson
noise limit. The result provides experimental evidence that magnetic near field
noise near the superconductor is strongly suppressed. Such long atomic spin
coherence times near superconductors open the way towards the development of
coherently coupled cold atom / solid state hybrid quantum systems with
potential applications in quantum information processing and precision force
sensing.Comment: Major revisions of the text for submission to New Journal of Physics
8 pages, 4 figure
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