464 research outputs found
Low-temperature specific heat for ferromagnetic and antiferromagnetic orders in CaRu1-xMnxO3
Low-temperature specific heat of CaRu1-xMnxO3 was measured to clarify the
role of d electrons in ferromagnetic and antiferromagnetic orders observed
above x=0.2. Specific heat divided by temperature C_p/T is found to roughly
follow a T^2 function, and relatively large magnitudes of electronic specific
heat coefficient gamma were obtained in wide x range. In particular, gamma is
unchanged from the value at x=0 (84 mJ/K^2 mol) in the paramagnetic state for
x<=0.1, but linearly reduced with increasing x above x= 0.2. These features of
gamma strongly suggest that itinerant d electrons are tightly coupled with the
evolution of magnetic orders in small and intermediate Mn concentrations.Comment: 4 pages, 2 figures, to be published in J. Phys.: Conf. Ser. (SCES
2011, Cambridge, UK
Rogers-Szego polynomials and Hall-Littlewood symmetric functions
We use Rogers-Szego polynomials to unify some well-known identities for
Hall-Littlewood symmetric functions due to Macdonald and Kawanaka.Comment: 18 page
Iron Fluorescent Line Emission from Black Hole Accretion Disks with Magnetic Reconnection-Heated Corona
We investigate the iron K fluorescent line produced by hard X-ray
photons from magnetic reconnection-heated corona. The hot corona with
temperature being about K can irradiate the underlying disk with a
continuum X-ray spectrum produced via thermal Comptonization. Then the iron
atoms in the disk photoelectrically absorb X-ray photons and radiate K
line photons. Therefore, the activity of corona is responsible to the iron line
emission from the underlying disk. In previous studies, oversimplified X-ray
photon sources are often assumed above the disk in order to compute the iron
line profile or power-law line emissivity profiles are assumed with an index
being a free parameter. We adopt the more realistic corona model constructed by
Liu et al. in which the corona is heated by magnetic energy released through
the reconnection of magnetic flux loops and which has no free parameter. Then
the accretion energy is dominantly dissipated in the corona, in which X-ray
photons are efficiently produced and irradiate the underlying disk. We find the
local emmisivity of iron line on the disk is approximated as . The iron line profiles derived from this model
give excellent fits to the observational data of MCG-6-30-15 with the profiles
derived theoretically for for energy band 4-7keV. Possible
origins of line variability are briefly discussed.Comment: 17 pages, 7 figures, accepted for publication in Ap
Temperature Dependent Polarized XANES Spectra for Zn-doped LSCO system
The cuprates seem to exhibit statistics, dimensionality and phase transitions
in novel ways. The nature of excitations [i.e. quasiparticle or collective],
spin-charge separation, stripes [static and dynamics], inhomogeneities,
psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in
these materials must be consistently understood. Zn-doped LSCO single crystal
were grown by TSFZ technique. Temperature dependent Polarized XANES [near edge
local structure] spectra were measured at the BL13-B1 [Photon Factory] in the
Flourescence mode from 10 K to 300 K. Since both stripes and nonmagnetic Zn
impurities substituted for Cu give rise to inhomogeneous charge and spin
distribution it is interesting to understand the interplay of Zn impurities and
stripes. To understand these points we have used Zn-doping and some of the
results obtained are as follows: The spectra show a strong dependence with
respect to the polarization angle, , as is evident at any temperature
by comparing the spectra where the electric field vector is parallel with
ab-plane to the one where it is parallel to the c-axis. By using the XANES
[temperature] difference spectra we have determined T* [experimentally we find,
T* 160-170 K] for this sample. The XANES difference spectra shows
that the changes in XANES features are larger in the ab-plane than the c-axis,
this trend is expected since zinc is doped in the ab-plane at the copper site.
Our study also complements the results in literature namely that zinc doping
does not affect the c-axis transport.Comment: To appear in Physica C [ISS2001 Special Issue], related talk
presented at ISS2001 as PC-16, 10 pages revtex and 7 pages of figures (pdf
Neutrino Cooled Disk and Its Stability
We investigate the structure and stability of hypercritical accretion flows
around stellar-mass black holes, taking into account neutrino cooling, lepton
conservation, and firstly a realistic equation of state in order to properly
treat the dissociation of nuclei. We obtain the radial distributions of
physical properties, such as density, temperature and electron fraction, for
various mass accretion rates . We find that,
depending on mass accretion rates, different physics affect considerably the
structure of the disk; most important physics is (1) the photodissociation of
nuclei around for relatively low mass accretion rates
(), (2) efficient neutrino cooling
around for moderately high mass accretion rate (), and (3) neutrino trapping () for
very high mass accretion rate (). We
also investigate the stability of hypercritical accretion flows by drawing the
thermal equilibrium curves, and find that efficient neutrino cooling makes the
accretion flows rather stable against both thermal and viscous modes.Comment: 26 pages, 28 figures, Accepted for publication in Ap
Clear Experimental Signature of Charge-Orbital density wave in NdCaMnO
Single Crystals of NdCaMnO have been prepared by the
travelling floating-zone method, and possible evidence of a charge -orbital
density wave in this material presented earlier [PRB68,092405 (2003)] using
High Resolution Electron Microscopy [HRTEM] and Electron Diffraction [ED]. In
the current note we present direct evidence of charge-orbital ordering in this
material using heat capacity measurements. Our heat capacity measurements
indicate a clear transition consistent with prior observation. We find two main
transitions, one at temperature K, and other at
K. In addition, we may also conclude that there is a strong electron-phonon
coupling in this material.Comment: 7 pages, 8 figure
Twisted Frobenius-Schur indicators for Hopf algebras
The classical Frobenius-Schur indicators for finite groups are character sums
defined for any representation and any integer m greater or equal to 2. In the
familiar case m=2, the Frobenius-Schur indicator partitions the irreducible
representations over the complex numbers into real, complex, and quaternionic
representations. In recent years, several generalizations of these invariants
have been introduced. Bump and Ginzburg, building on earlier work of Mackey,
have defined versions of these indicators which are twisted by an automorphism
of the group. In another direction, Linchenko and Montgomery have defined
Frobenius-Schur indicators for semisimple Hopf algebras. In this paper, the
authors construct twisted Frobenius-Schur indicators for semisimple Hopf
algebras; these include all of the above indicators as special cases and have
similar properties.Comment: 12 pages. Minor revision
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