888 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
Cryostat to provide a solid deuterium layer in a plastic shell for the Gekko XII glass laser system
Copyright 1992 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments, 63(6), 3378-3383, 1992 and may be found at http://dx.doi.org/10.1063/1.114255
Anomalous Stability of nu=1 Bilayer Quantum Hall State
We have studied the fractional and integer quantum Hall (QH) effects in a
high-mobility double-layer two-dimensional electron system. We have compared
the "stability" of the QH state in balanced and unbalanced double quantum
wells. The behavior of the n=1 QH state is found to be strikingly different
from all others. It is anomalously stable, though all other states decay, as
the electron density is made unbalanced between the two quantum wells. We
interpret the peculiar features of the nu=1 state as the consequences of the
interlayer quantum coherence developed spontaneously on the basis of the
composite-boson picture.Comment: 5 pages, 6 figure
Telerobotics test bed for space structure assembly
A cooperative research on super long distance space telerobotics is now in progress both in Japan and USA. In this program. several key features will be tested, which can be applicable to the control of space robots as well as to terrestrial robots. Local (control) and remote (work) sites will be shared between Electrotechnical Lab (ETL) of MITI in Japan and Jet Propulsion Lab (JPL) in USA. The details of a test bed for this international program are discussed in this report
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
Phase Transition in \nu=2 Bilayer Quantum Hall State
The Hall-plateau width and the activation energy were measured in the bilayer
quantum Hall state at filling factor \nu=2, 1 and 2/3, by changing the total
electron density and the density ratio in the two quantum wells. Their behavior
are remarkably different from one to another. The \nu=1 state is found stable
over all measured range of the density difference, while the \nu=2/3$ state is
stable only around the balanced point. The \nu=2 state, on the other hand,
shows a phase transition between these two types of the states as the electron
density is changed.Comment: 5 pages including figures, RevTe
Cooperative Effect of Coulomb Interaction and Electron-Phonon Coupling on the Heavy Fermion State in the Two-Orbital Periodic Anderson Model
We investigate the two-orbital periodic Anderson model, where the local
orbital fluctuations of f-electrons couple with a two-fold degenerate
Jahn-Teller phonon, by using the dynamical mean-field theory. It is found that
the heavy fermion state caused by the Coulomb interaction between f-electrons U
is largely enhanced due to the electron-phonon coupling g, in contrast to the
case with the single-orbital periodic Anderson model where the effects of U and
g compete to each other. In the heavy fermion state for large and g, both
the orbital and lattice fluctuations are enhanced, while the charge (valence)
and spin fluctuations are suppressed. In the strong coupling regime, a sharp
soft phonon mode with a large spectral weight is observed for small U, while a
broad soft phonon mode with a small spectral weight is observed for large U.
The cooperative effect of U and g for half-filling with two f-electrons per
atom is more pronounced than that for quarter-filling with .Comment: 8 pages, 11 figures, accepted for publication in JPS
Effects of an anionic surfactant (FFD-6) on the energy and information flow between a primary producer (Scenedesmus obliquus) and a consumer (Daphnia magna)
The effects of a commercially available anionic surfactant solution (FFD-6) on growth and morphology of a common green alga (Scenedesmus obliquus) and on survival and clearance rates of the water flea Daphnia magna were studied. The surfactant-solution elicited a morphological response (formation of colonies) in Scenedesmus at concentrations of 10â100 Οl lâ1 that were far below the No Observed Effect Concentration (NOEC) value of 1,000 Îźl lâ1 for growth inhibition. The NOEC-value of FFD-6 for colony-induction was 3 Οl lâ1. Daphnia survival was strongly affected by FFD-6, yielding LC50â24h and LC50â48h of 148 and 26 Οl lâ1, respectively. In addition, clearance rates of Daphnia feeding on unicellular Scenedesmus were inhibited by FFD-6, yielding a 50% inhibition (EC50â1.5h) at 5.2 Οl lâ1 with a NOEC of 0.5 Οl lâ1. When Daphnia were offered FFD-6-induced food in which eight-celled colonies (43 Ă 29 Οm) were most abundant, clearance rates (~0.14 ml ind.â1 hâ1) were only 25% the rates of animals that were offered non-induced unicellular (15 Ă 5 Οm) Scenedesmus (~0.56 ml ind.â1 hâ1). As FFD-6 concentrations in the treated food used in the experiments were far below the NOEC for clearance rate inhibition, it is concluded that the feeding rate depression was caused by the altered morphology of the Scenedesmus moving them out of the feeding window of the daphnids. The surfactant evoked a response in Scenedesmus that is similar to the natural chemically induced defensive reaction against grazers and could disrupt the natural information conveyance between these plankton organisms
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