131,306 research outputs found
A hidden constant in the anomalous Hall effect of a high-purity magnet MnSi
Measurements of the Hall conductivity in MnSi can provide incisive tests of
theories of the anomalous Hall (AH) effect, because both the mean-free-path and
magnetoresistance (MR) are unusually large for a ferromagnet. The large MR
provides an accurate way to separate the AH conductivity from
the ordinary Hall conductivity . Below the Curie temperature
, is linearly proportional to (magnetization) with a
proportionality constant that is independent of both and . In
particular, remains a constant while changes by a factor
of 100 between 5 K and . We discuss implications of the hidden constancy
in .Comment: 5 pages, 4 figures. Minor change
Comment on ''the controlled charge ordering and evidence of the metallic state in PrCaMnO films''
In a recent paper (2000 \QTR{it}{J. Phys.: Condens. Matter} \QTR{bf}{12}
L133) Lee \QTR{it}{et al.} have studied the transport properties of
PrCaMnO thin films. They claimed that they are able to
controlled the charge-ordered (CO) state by the lattice strains. We propose
herein another alternative since another indexation of the orientation of the
film can be found leading to almost no distortion of the cell, as compared to
the bulk compound.Comment: 2 page
Chiral symmetry breaking in a uniform external magnetic field II. Symmetry restoration at high temperatures and chemical potentials
Chiral symmetry is dynamically broken in quenched, ladder QED at weak gauge
couplings when an external magnetic field is present. In this paper, we show
that chiral symmetry is restored above a critical chemical potential and the
corresponding phase transition is of first order. In contrast, the chiral
symmetry restoration at high temperatures (and at zero chemical potential) is a
second order phase transition.Comment: Latex; 12 pages; 8 postscript figures include
An Analysis of the Decay with Predictions from Heavy Quark and Chiral Symmetry
This paper considers the implications of the heavy quark and chiral
symmetries for the semi-leptonic decay . The general kinematic analysis for decays of the form {\sl
pseudoscalar meson vector meson pseudoscalar meson lepton
anti-lepton} is presented. This formalism is applied to the above exclusive
decay which allows the differential decay rate to be expressed in a form that
is ideally suited for the experimental determination of the different form
factors for the process through angular distribution measurements. Heavy quark
and chiral symmetry predictions for the form factors are presented, and the
differential decay rate is calculated in the kinematic region where chiral
perturbation theory is valid.Comment: 15 pages, uses jytex.tex and tables.tex; 3 figures not included but
available on reques
A possible observational bias in the estimation of the virial parameter in virialized clumps
The dynamics of massive clumps, the environment where massive stars
originate, is still unclear. Many theories predict that these regions are in a
state of near-virial equilibrium, or near energy equi-partition, while others
predict that clumps are in a sub-virial state. Observationally, the majority of
the massive clumps are in a sub-virial state with a clear anti-correlation
between the virial parameter and the mass of the clumps ,
which suggests that the more massive objects are also the more gravitationally
bound. Although this trend is observed at all scales, from massive clouds down
to star-forming cores, theories do not predict it. In this work we show how,
starting from virialized clumps, an observational bias is introduced in the
specific case where the kinetic and the gravitational energies are estimated in
different volumes within clumps and how it can contribute to the spurious
anti-correlation in these data. As a result, the observed
effective virial parameter , and in some
circumstances it might not be representative of the virial state of the
observed clumps.Comment: A&A letter, accepte
Kondo Insulator description of spin state transition in FeSb2
The thermal expansion and heat capacity of FeSb2 at ambient pressure agrees
with a picture of a temperature induced spin state transition within the Fe
t_{2g} multiplet. However, high pressure powder diffraction data show no sign
of a structural phase transition up to 7GPa. A bulk modulus B=84(3)GPa has been
extracted and the temperature dependence of the Gruneisen parameter has been
determined. We discuss here the relevance of a Kondo insulator description for
this material.Comment: Physical Review B in press (2005
Diamagnetism and flux creep in bilayer exciton superfluids
We discuss the diamagnetism induced in an isolated quantum Hall bilayer with
total filling factor one by an in-plane magnetic field. This is a signature of
counterflow superfluidity in these systems. We calculate magnetically induced
currents in the presence of pinned vortices nucleated by charge disorder, and
predict a history-dependent diamagnetism that could persist on laboratory
timescales. For current samples we find that the maximum in-plane moment is
small, but with stronger tunneling the moments would be measurable using torque
magnetometry. Such experiments would allow the persistent currents of a
counterflow superfluid to be observed in an electrically isolated bilayer.Comment: 8 pages, 2 figures. v2: updated to accepted version, extended
presentatio
Noncommutative BTZ Black Hole in Polar Coordinates
Based on the equivalence between the three dimensional gravity and the
Chern-Simons theory, we obtain a noncommutative BTZ black hole solution as a
solution of noncommutative Chern-Simons theory using the
Seiberg-Witten map. The Seiberg-Witten map is carried out in a noncommutative
polar coordinates whose commutation relation is equivalent to the usual
canonical commutation relation in the rectangular coordinates up to first order
in the noncommutativity parameter . The solution exhibits a
characteristic of noncommutative polar coordinates in such a way that the
apparent horizon and the Killing horizon coincide only in the non-rotating
limit showing the effect of noncommutativity between the radial and angular
coordinates.Comment: 14 pages, V2: minor changes, v3: reduced for clarification, a
reference adde
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