180 research outputs found
Strong suppression of superconductivity by divalent Ytterbium Kondo-holes in CeCoIn_5
To study the nature of partially substituted Yb-ions in a Ce-based Kondo
lattice, we fabricated high quality Ce_{1-x}Yb_xCoIn_5 epitaxial thin films
using molecular beam epitaxy. We find that the Yb-substitution leads to a
linear decrease of the unit cell volume, indicating that Yb-ions are divalent
forming Kondo-holes in Ce_{1-x}Yb_xCoIn_5, and leads to a strong suppression of
the superconductivity and Kondo coherence. These results, combined with the
measurements of Hall effect, indicate that Yb-ions act as nonmagnetic impurity
scatters in the coherent Kondo lattice without serious suppression of the
antiferromagnetic fluctuations. These are in stark contrast to previous studies
performed using bulk single crystals, which claim the importance of valence
fluctuations of Yb-ions. The present work also highlights the suitability of
epitaxial films in the study of the impurity effect on the Kondo lattice.Comment: 5 pages, 4 figure
Controllable Rashba spin-orbit interaction in artificially engineered superlattices involving the heavy-fermion superconductor CeCoIn5
By using a molecular beam epitaxy technique, we fabricate a new type of
superconducting superlattices with controlled atomic layer thicknesses of
alternating blocks between heavy fermion superconductor CeCoIn_5, which
exhibits a strong Pauli pair-breaking effect, and nonmagnetic metal YbCoIn_5.
The introduction of the thickness modulation of YbCoIn_5 block layers breaks
the inversion symmetry centered at the superconducting block of CeCoIn_5. This
configuration leads to dramatic changes in the temperature and angular
dependence of the upper critical field, which can be understood by considering
the effect of the Rashba spin-orbit interaction arising from the inversion
symmetry breaking and the associated weakening of the Pauli pair-breaking
effect. Since the degree of thickness modulation is a design feature of this
type of superlattices, the Rashba interaction and the nature of pair-breaking
are largely tunable in these modulated superlattices with strong spin-orbit
coupling.Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let
Lower Critical Fields of Superconducting PrFeAsO Single Crystals
We have studied the lower critical fields H_{c1} of superconducting iron
oxipnictide PrFeAsO_{1-y} single crystals for H parallel and perpendicular to
the ab-planes. Measurements of the local magnetic induction at positions
straddling the sample edge by using a miniature Hall-sensor array clearly
resolve the first flux penetration from the Meissner state. The temperature
dependence of H_{c1} for H || c is well scaled by the in-plane penetration
depth without showing any unusual behavior, in contrast to previous reports.
The anisotropy of penetration lengths at low temperatures is estimated to be ~
2.5, which is much smaller than the anisotropy of the coherence lengths. This
is indicative of multiband superconductivity in this system, in which the
active band for superconductivity is more anisotropic. We also point out that
the local induction measured at a position near the center of the crystal,
which has been used in a number of reports for the determination of H_{c1},
might seriously overestimate the obtained H_{c1}-value.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
Diphoton Production at Hadron Colliders and New Contact Interactions
We explore the capability of the Tevatron and LHC to place limits on the
possible existence of flavor-independent contact
interactions which can lead to an excess of diphoton events with large
invariant masses. Assuming no departure from the Standard Model is observed, we
show that the Tevatron will eventually be able to place a lower bound of
0.5-0.6 TeV on the scale associated with this new contact interaction. At the
LHC, scales as large as 3-6 TeV may be probed with suitable detector cuts and
an integrated luminosity of .Comment: LaTex, 12pages plus 5 figures(available on request), SLAC-PUB-657
Anomalous Upper Critical Field in CeCoIn_5/YbCoIn_5 Superlattices with a Rashba-type Heavy Fermion Interface
We report a highly unusual angular variation of the upper critical field
(H_c2) in epitaxial superlattices CeCoIn_5(n)/YbCoIn_5(5), formed by
alternating layers of n and a 5 unit-cell thick heavy-fermion superconductor
CeCoIn_5 with a strong Pauli effect and normal metal YbCoIn_5, respectively.
For the n=3 superlattice, H_{c2}(\theta) changes smoothly as a function of the
field angle \theta. However, close to the superconducting transition
temperature, H_{c2}(\theta) exhibits a cusp near the parallel field (\theta=0
deg). This cusp behavior disappears for n=4 and 5 superlattices. This sudden
disappearance suggests the relative dominance of the orbital depairing effect
in the n=3 superlattice, which may be due to the suppression of the Pauli
effect in a system with local inversion symmetry breaking. Taking into account
the temperature dependence of H_{c2}(\theta) as well, our results suggest that
some exotic superconducting states, including a helical superconducting state,
might be realized at high magnetic fields.Comment: 5 pages, 5 figure
A Measurement of the Cross Section in Two-Photon Processes
We have measured the inclusive production cross section in a
two-photon collision at the TRISTAN collider. The mean of
the collider was 57.16 GeV and the integrated luminosity was 150 . The
differential cross section () was obtained in the
range between 1.6 and 6.6 GeV and compared with theoretical predictions, such
as those involving direct and resolved photon processes.Comment: 8 pages, Latex format (article), figures corrected, published in
Phys. Rev. D 50 (1994) 187
Quantitative Characterization of the Filiform Mechanosensory Hair Array on the Cricket Cercus
Crickets and other orthopteran insects sense air currents with a pair of abdominal appendages resembling antennae, called cerci. Each cercus in the common house cricket Acheta domesticus is approximately 1 cm long, and is covered with 500 to 750 filiform mechanosensory hairs. The distribution of the hairs on the cerci, as well as the global patterns of their movement vectors, have been characterized semi-quantitatively in studies over the last 40 years, and have been shown to be very stereotypical across different animals in this species. Although the cercal sensory system has been the focus of many studies in the areas of neuroethology, development, biomechanics, sensory function and neural coding, there has not yet been a quantitative study of the functional morphology of the receptor array of this important model system.We present a quantitative characterization of the structural characteristics and functional morphology of the cercal filiform hair array. We demonstrate that the excitatory direction along each hair's movement plane can be identified by features of its socket that are visible at the light-microscopic level, and that the length of the hair associated with each socket can also be estimated accurately from a structural parameter of the socket. We characterize the length and directionality of all hairs on the basal half of a sample of three cerci, and present statistical analyses of the distributions.The inter-animal variation of several global organizational features is low, consistent with constraints imposed by functional effectiveness and/or developmental processes. Contrary to previous reports, however, we show that the filiform hairs are not re-identifiable in the strict sense
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