26,414 research outputs found
Compensation of Effective Field in the Field-Induced Superconductor k-(BETS)2FeBr4 Observed by 77Se NMR
We report results of 77Se NMR frequency shift in the normal state of the
organic charge-transfer-salt k-(BETS)2FeBr4 which shows magnetic field-induced
superconductivity (FISC). From a simple mean field analysis, we determined the
field and the temperature dependences of the magnetization m_{pi} of the \pi
conduction electrons on BETS molecules. We found that the Fe spins are
antiferromagnetically coupled to the pi electrons and determined the exchange
field to be J = -2.3T/mu_B. The exchange field from the fully saturated Fe
moments (5 mu_B) is compensated by an external field of 12T. This is close to
the central field of the FISC phase, consistent with the Jaccarino-Peter local
field-compensation mechanism for FISC (Phys. Rev. Lett. 9, 290 (1962))
Multiscale expansion of the lattice potential KdV equation on functions of infinite slow-varyness order
We present a discrete multiscale expansion of the lattice potential
Korteweg-de Vries (lpKdV) equation on functions of infinite order of
slow-varyness. To do so we introduce a formal expansion of the shift operator
on many lattices holding at all orders. The lowest secularity condition from
the expansion of the lpKdV equation gives a nonlinear lattice equation,
depending on shifts of all orders, of the form of the nonlinear Schr\"odinger
(NLS) equationComment: 9 pages, submitted to Journ. Phys.
The Law and Economics of Proportionality in Discovery
This paper analyzes the proportionality standard in discovery. Many believe the Advisory Committee\u27s renewed emphasis on this standard has the potential to infuse litigation practice with considerably more attention to questions related to the costs and benefits of discovery. We discuss the history and rationale of proportionality\u27s inclusion in Rule 26, adopting an analytical framework that focuses on how costs and benefits can diverge in litigation generally, and discovery in particular. Finally, we use this framework to understand the mechanics and challenges involved in deploying the six factors included in the proportionality standard. Throughout, we emphasize that the proportionality standard requires both difficult-to-answer positive questions and unavoidably normative judgments
Properties of the quaternary half-metal-type Heusler alloy CoMnFeSi
This work reports on the bulk properties of the quaternary Heusler alloy
CoMnFeSi with the Fe concentration . All samples, which
were prepared by arc melting, exhibit long range order over the complete
range of Fe concentration. Structural and magnetic properties of
CoMnFeSi Heusler alloys were investigated by means of X-ray
diffraction, high and low temperature magnetometry, M{\"o\ss}bauer
spectroscopy, and differential scanning calorimetry. The electronic structure
was explored by means of high energy photo emission spectroscopy at about 8 keV
photon energy. This ensures true bulk sensitivity of the measurements. The
magnetization of the Fe doped Heusler alloys is in agreement with the values of
the magnetic moments expected for a Slater-Pauling like behavior of
half-metallic ferromagnets. The experimental findings are discussed on the hand
of self-consistent calculations of the electronic and magnetic structure. To
achieve good agreement with experiment, the calculations indicate that on-site
electron-electron correlation must be taken into account, even at low Fe
concentration. The present investigation focuses on searching for the
quaternary compound where the half-metallic behavior is stable against outside
influences. Overall, the results suggest that the best candidate may be found
at an iron concentration of about 50%.Comment: 26 pages, 9 figures Phys. Rev. B accepte
Axiomatic Holonomy Maps and Generalized Yang-Mills Moduli Space
This article is a follow-up of ``Holonomy and Path Structures in General
Relativity and Yang-Mills Theory" by Barrett, J. W. (Int.J.Theor.Phys., vol.30,
No.9, 1991). Its main goal is to provide an alternative proof of this part of
the reconstruction theorem which concerns the existence of a connection. A
construction of connection 1-form is presented. The formula expressing the
local coefficients of connection in terms of the holonomy map is obtained as an
immediate consequence of that construction. Thus the derived formula coincides
with that used in "On Loop Space Formulation of Gauge Theories" by Chan, H.-M.,
Scharbach, P. and Tsou S.T. (Ann.Phys., vol.167, 454-472, 1986). The
reconstruction and representation theorems form a generalization of the fact
that the pointed configuration space of the classical Yang-Mills theory is
equivalent to the set of all holonomy maps. The point of this generalization is
that there is a one-to-one correspondence not only between the holonomy maps
and the orbits in the space of connections, but also between all maps from the
loop space on to group fulfilling some axioms and all possible
equivalence classes of bundles with connection, where the equivalence
relation is defined by bundle isomorphism in a natural way.Comment: amslatex, 7 pages, no figure
New electronic orderings observed in cobaltates under the influence of misfit periodicities
We study with ARPES the electronic structure of CoO2 slabs, stacked with
rock-salt (RS) layers exhibiting a different (misfit) periodicity. Fermi
Surfaces (FS) in phases with different doping and/or periodicities reveal the
influence of the RS potential on the electronic structure. We show that these
RS potentials are well ordered, even in incommensurate phases, where STM images
reveal broad stripes with width as large as 80\AA. The anomalous evolution of
the FS area at low dopings is consistent with the localization of a fraction of
the electrons. We propose that this is a new form of electronic ordering,
induced by the potential of the stacked layers (RS or Na in NaxCoO2) when the
FS becomes smaller than the Brillouin Zone of the stacked structure
Direct observation of localization in the minority-spin-band electrons of magnetite below the Verwey temperature
Two-dimensional spin-uncompensated momentum density distributions, s, were reconstructed in magnetite at 12K and 300K from
several measured directional magnetic Compton profiles. Mechanical de-twinning
was used to overcome severe twinning in the single crystal sample below the
Verwey transition. The reconstructed in the first
Brillouin zone changes from being negative at 300 K to positive at 12 K. This
result provides the first clear evidence that electrons with low momenta in the
minority spin bands in magnetite are localized below the Verwey transition
temperature.Comment: 13 pages, 4 figures, accepted in Physical Review
DNA Nucleobase Synthesis at Titan Atmosphere Analog by Soft X-rays
Titan, the largest satellite of Saturn, has an atmosphere chiefly made up of
N2 and CH4 and includes traces of many simple organic compounds. This
atmosphere also partly consists of haze and aerosol particles which during the
last 4.5 gigayears have been processed by electric discharges, ions, and
ionizing photons, being slowly deposited over the Titan surface. In this work,
we investigate the possible effects produced by soft X-rays (and secondary
electrons) on Titan aerosol analogs in an attempt to simulate some prebiotic
photochemistry. The experiments have been performed inside a high vacuum
chamber coupled to the soft X-ray spectroscopy beamline at the Brazilian
Synchrotron Light Source, Campinas, Brazil. In-situ sample analyses were
performed by a Fourier transform infrared spectrometer. The infrared spectra
have presented several organic molecules, including nitriles and aromatic CN
compounds. After the irradiation, the brownish-orange organic residue (tholin)
was analyzed ex-situ by gas chromatographic (GC/MS) and nuclear magnetic
resonance (1H NMR) techniques, revealing the presence of adenine (C5H5N5), one
of the constituents of the DNA molecule. This confirms previous results which
showed that the organic chemistry on the Titan surface can be very complex and
extremely rich in prebiotic compounds. Molecules like these on the early Earth
have found a place to allow life (as we know) to flourish.Comment: To appear in Journal of Physical Chemistry A.; Number of pages: 6;
Number of Figures: 5; Number of Tables: 1; Number of references:49; Full
paper at http://pubs.acs.org/doi/abs/10.1021/jp902824
Superconductivity in an organic insulator at very high magnetic fields
We investigate by electrical transport the field-induced superconducting
state (FISC) in the organic conductor -(BETS)FeCl. Below 4 K,
antiferromagnetic-insulator, metallic, and eventually superconducting (FISC)
ground states are observed with increasing in-plane magnetic field. The FISC
state survives between 18 and 41 T, and can be interpreted in terms of the
Jaccarino-Peter effect, where the external magnetic field {\em compensates} the
exchange field of aligned Fe ions. We further argue that the Fe
moments are essential to stabilize the resulting singlet, two-dimensional
superconducting stateComment: 9 pages 3 figure
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