219 research outputs found
Wide-field quantitative magnetic imaging of superconducting vortices using perfectly aligned quantum sensors
Various techniques have been applied to visualize superconducting vortices,
providing clues to their electromagnetic response. Here, we present a
wide-field, quantitative imaging of the stray field of the vortices in a
superconducting thin film using perfectly aligned diamond quantum sensors. Our
analysis, which mitigates the influence of the sensor inhomogeneities,
visualizes the magnetic flux of single vortices in YBaCuO
with an accuracy of . The obtained vortex shape is consistent with
the theoretical model, and penetration depth and its temperature dependence
agree with previous studies, proving our technique's accuracy and broad
applicability. This wide-field imaging, which in principle works even under
extreme conditions, allows the characterization of various superconductors
Vector form factor in K_l3 semileptonic decay with two flavors of dynamical domain-wall quarks
We calculate the vector form factor in K \to \pi l \nu semileptonic decays at
zero momentum transfer f_+(0) from numerical simulations of two-flavor QCD on
the lattice. Our simulations are carried out on 16^3 \times 32 at a lattice
spacing of a \simeq 0.12 fm using a combination of the DBW2 gauge and the
domain-wall quark actions, which possesses excellent chiral symmetry even at
finite lattice spacings. The size of fifth dimension is set to L_s=12, which
leads to a residual quark mass of a few MeV. Through a set of double ratios of
correlation functions, the form factor calculated on the lattice is accurately
interpolated to zero momentum transfer, and then is extrapolated to the
physical quark mass. We obtain f_+(0)=0.968(9)(6), where the first error is
statistical and the second is the systematic error due to the chiral
extrapolation. Previous estimates based on a phenomenological model and chiral
perturbation theory are consistent with our result. Combining with an average
of the decay rate from recent experiments, our estimate of f_+(0) leads to the
Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V_{us}|=0.2245(27), which is
consistent with CKM unitarity. These estimates of f_+(0) and |V_{us}| are
subject to systematic uncertainties due to the finite lattice spacing and
quenching of strange quarks, though nice consistency in f_+(0) with previous
lattice calculations suggests that these errors are not large.Comment: 23 pages, 11 figures, 7 tables, RevTeX4; v3: one table added, results
and conclusions unchanged, final version to appear in Phys.Rev.
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