800 research outputs found
Superconductivity in the New Platinum Germanides MPt4Ge12 (M = Rare-earth and Alkaline-earth Metals) with Filled Skutterudite Structure
New germanium-platinum compounds with the filled-skutterudite crystal
structure were synthesized. The structure and composition were investigated by
X-ray diffraction and microprobe analysis. Magnetic susceptibility, specific
heat, and electrical resistivity measurements evidence superconductivity in
LaPt4Ge12 and PrPt4Ge12 below 8.3K. The parameters of the normal and
superconducting states were established. Strong coupling and a crystal electric
field singlet groundstate is found for the Pr compound. Electronic structure
calculations show a large density of states at the Fermi level. Similar
behavior with lower T_c was observed for SrPt4Ge12 and BaPt4Ge12.Comment: RevTeX, 4 figures, submitted to Physical Review Letters July 12, 200
Ising-type Magnetic Anisotropy in CePdAs
We investigated the anisotropic magnetic properties of CePdAs by
magnetic, thermal and electrical transport studies. X-ray diffraction confirmed
the tetragonal ThCrSi-type structure and the high-quality of the single
crystals. Magnetisation and magnetic susceptibility data taken along the
different crystallographic directions evidence a huge crystalline electric
field (CEF) induced Ising-type magneto-crystalline anisotropy with a large
-axis moment and a small in-plane moment at low temperature. A detailed CEF
analysis based on the magnetic susceptibility data indicates an almost pure
CEF ground-state doublet with the dominantly
and the doublets at 290 K and 330
K, respectively. At low temperature, we observe a uniaxial antiferromagnetic
(AFM) transition at K with the crystallographic -direction being
the magnetic easy-axis. The magnetic entropy gain up to reaches almost
indicating localised -electron magnetism without significant
Kondo-type interactions. Below , the application of a magnetic field along
the -axis induces a metamagnetic transition from the AFM to a
field-polarised phase at T, exhibiting a text-book example
of a spin-flip transition as anticipated for an Ising-type AFM.Comment: 9 Pages, 8 figure
The impact of chromosomes and centrosomes on spindle assembly as observed in living cells.
Superfluid Density and Energy Gap-Function of Superconducting PrPt4Ge12
The filled skutterudite superconductor PrPt4Ge12 was studied in muon-spin
rotation (muSR), specific heat, and electrical resistivity experiments. The
continuous increase of the superfluid density with decreasing temperature and
the dependence of the magnetic penetration depth \lambda on the magnetic field
obtained by means of muSR, as well as the observation of a T^3 dependence of
the electronic specific heat establish the presence of point-like nodes in the
superconducting energy gap. The energy gap was found to be well described by
\Delta =\Delta_0| k_x - ik_y| or \Delta = \Delta_0(1 - k_y^4) functional forms,
similar to that obtained for another skutterudite superconductor, PrOs4Sb12.
The gap to T_c ratios were estimated to be \Delta_0/k_BT_c = 2.68(5) and
2.29(5), respectively.Comment: 4 pages, 5 figure
Fluctuation-Driven Quantum Phase Transitions in Clean Itinerant Ferromagnets
The quantum phase transition in clean itinerant ferromagnets is analyzed. It
is shown that soft particle-hole modes invalidate Hertz's mean-field theory for
. A renormalized mean-field theory predicts a fluctuation-induced
first order transition for , whose stability is analyzed by
renormalization group techniques. Depending on microscopic parameter values,
the first order transition can be stable, or be pre-empted by a
fluctuation-induced second order transition. The critical behavior at the
latter is determined. The results are in agreement with recent experiments.Comment: 4 pp., REVTeX, no figs; final version as publishe
Kinetochore chemistry is sensitive to tension and may link mitotic forces to a cell cycle checkpoint.
Nature of the Quantum Phase Transition in Clean, Itinerant Heisenberg Ferromagnets
A comprehensive theory of the quantum phase transition in clean, itinerant
Heisenberg ferromagnets is presented. It is shown that the standard mean-field
description of the transition is invalid in spatial dimensions due to
the existence of soft particle-hole excitations that couple to the order
parameter fluctuations and lead to an upper critical dimension . A
generalized mean-field theory that takes these additional modes into account
predicts a fluctuation-induced first-order transition. In a certain parameter
regime, this first-order transition in turn is unstable with respect to a
fluctuation-induced second-order transition. The quantum ferromagnetic
transition may thus be either of first or of second-order, in agreement with
experimental observations. A detailed discussion is given of the stability of
the first-order transition, and of the critical behavior at the
fluctuation-induced second-order transition. In , the latter is mean
field-like with logarithmic corrections to scaling, and in it can be
controlled by means of a expansion.Comment: 15 pp., revtex4, 6 eps figs; final version as publishe
The FORS Deep Field: Field selection, photometric observations and photometric catalog
The FORS Deep Field project is a multi-colour, multi-object spectroscopic
investigation of an approx. 7 times 7 region near the south galactic pole based
mostly on observations carried out with the FORS instruments attached to the
VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this
study is to improve our understanding of the formation and evolution of
galaxies in the young Universe. In this paper the field selection, the
photometric observations, and the data reduction are described. The source
detection and photometry of objects in the FORS Deep Field is discussed in
detail. A combined B and I selected UBgRIJKs photometric catalog of 8753
objects in the FDF is presented and its properties are briefly discussed. The
formal 50% completeness limits for point sources, derived from the co-added
images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57 in U, B, g, R,
I, J and Ks (Vega-system), respectively. A comparison of the number counts in
the FORS Deep Field to those derived in other deep field surveys shows very
good agreement.Comment: 15 pages, 11 figures (included), accepted for publication in A&
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