9,490 research outputs found
Magnetic-Field Induced Gap in One-Dimensional Antiferromagnet KCuGaF
Magnetic susceptibility and specific heat measurements in magnetic fields
were performed on an one-dimensional antiferromagnet KCuGaF.
Exchange interaction was evaluated as K. However, no
magnetic ordering was observed down to 0.46 K. It was found that an applied
magnetic field induces a staggered magnetic susceptibility obeying the Curie
law and an excitation gap, both of which should be attributed to the
antisymmetric interaction of the Dzyaloshinsky-Moriya type and/or the staggered
-tensor. With increasing magnetic field , the gap increases almost in
proportion to .Comment: Submitted to Proceedings of Research in High Magnetic Fiel
Pariah moonshine
Finite simple groups are the building blocks of finite symmetry. The effort
to classify them precipitated the discovery of new examples, including the
monster, and six pariah groups which do not belong to any of the natural
families, and are not involved in the monster. It also precipitated monstrous
moonshine, which is an appearance of monster symmetry in number theory that
catalysed developments in mathematics and physics. Forty years ago the pioneers
of moonshine asked if there is anything similar for pariahs. Here we report on
a solution to this problem that reveals the O'Nan pariah group as a source of
hidden symmetry in quadratic forms and elliptic curves. Using this we prove
congruences for class numbers, and Selmer groups and Tate--Shafarevich groups
of elliptic curves. This demonstrates that pariah groups play a role in some of
the deepest problems in mathematics, and represents an appearance of pariah
groups in nature.Comment: 20 page
Antisymmetrized molecular dynamics of wave packets with stochastic incorporation of Vlasov equation
On the basis of the antisymmetrized molecular dynamics (AMD) of wave packets
for the quantum system, a novel model (called AMD-V) is constructed by the
stochastic incorporation of the diffusion and the deformation of wave packets
which is calculated by Vlasov equation without any restriction on the one-body
distribution. In other words, the stochastic branching process in molecular
dynamics is formulated so that the instantaneous time evolution of the averaged
one-body distribution is essentially equivalent to the solution of Vlasov
equation. Furthermore, as usual molecular dynamics, AMD-V keeps the many-body
correlation and can naturally describe the fluctuation among many channels of
the reaction. It is demonstrated that the newly introduced process of AMD-V has
drastic effects in heavy ion collisions of 40Ca + 40Ca at 35 MeV/nucleon,
especially on the fragmentation mechanism, and AMD-V reproduces the
fragmentation data very well. Discussions are given on the interrelation among
the frameworks of AMD, AMD-V and other microscopic models developed for the
nuclear dynamics.Comment: 26 pages, LaTeX with revtex and epsf, embedded postscript figure
Electrochemical synthesis and properties of CoO2, the x = 0 phase of the AxCoO2 systems (A = Li, Na)
Single-phase bulk samples of the "exotic" CoO2, the x = 0 phase of the AxCoO2
systems (A = Li, Na), were successfully synthesized through electrochemical
de-intercalation of Li from pristine LiCoO2 samples. The samples of pure CoO2
were found to be essentially oxygen stoichiometric and possess a hexagonal
structure consisting of stacked triangular-lattice CoO2 layers only. The
magnetism of CoO2 is featured with a temperature-independent susceptibility of
the magnitude of 10-3 emu/mol Oe, being essentially identical to that of a
Li-doped phase, Li0.12CoO2. It is most likely that the CoO2 phase is a
Pauli-paramagnetic metal with itinerant electrons.Comment: 12 pages, 3 figure
Spin Polarization and Magneto-Coulomb Oscillations in Ferromagnetic Single Electron Devices
The magneto-Coulomb oscillation, the single electron repopulation induced by
external magnetic field, observed in a ferromagnetic single electron transistor
is further examined in various ferromagnetic single electron devices. In case
of double- and triple-junction devices made of Ni and Co electrodes, the single
electron repopulation always occurs from Ni to Co electrodes with increasing a
magnetic field, irrespective of the configurations of the electrodes. The
period of the magneto-Coulomb oscillation is proportional to the single
electron charging energy. All these features are consistently explained by the
mechanism that the Zeeman effect induces changes of the Fermi energy of the
ferromagnetic metal having a non-zero spin polarizations. Experimentally
determined spin polarizations are negative for both Ni and Co and the magnitude
is larger for Ni than Co as expected from band calculations.Comment: 4 pages, 3 figures, uses jpsj.sty, submitted to J. Phys. Soc. Jp
Antisymmetrized molecular dynamics with quantum branching processes for collisions of heavy nuclei
Antisymmetrized molecular dynamics (AMD) with quantum branching processes is
reformulated so that it can be applicable to the collisions of heavy nuclei
such as Au + Au multifragmentation reactions. The quantum branching process due
to the wave packet diffusion effect is treated as a random term in a
Langevin-type equation of motion, whose numerical treatment is much easier than
the method of the previous papers. Furthermore a new approximation formula,
called the triple-loop approximation, is introduced in order to evaluate the
Hamiltonian in the equation of motion with much less computation time than the
exact calculation. A calculation is performed for the Au + Au central
collisions at 150 MeV/nucleon. The result shows that AMD almost reproduces the
copious fragment formation in this reaction.Comment: 24 pages, 5 figures embedde
Electronic phase diagram of the layered cobalt oxide system, LixCoO2 (0.0 <= x <= 1.0)
Here we report the magnetic properties of the layered cobalt oxide system,
LixCoO2, in the whole range of Li composition, 0 <= x <= 1. Based on
dc-magnetic susceptibility data, combined with results of 59Co-NMR/NQR
observations, the electronic phase diagram of LixCoO2 has been established. As
in the related material NaxCoO2, a magnetic critical point is found to exist
between x = 0.35 and 0.40, which separates a Pauli-paramagnetic and a
Curie-Weiss metals. In the Pauli-paramagnetic regime (x <= 0.35), the
antiferromagnetic spin correlations systematically increase with decreasing x.
Nevertheless, CoO2, the x = 0 end member is a non-correlated metal in the whole
temperature range studied. In the Curie-Weiss regime (x >= 0.40), on the other
hand, various phase transitions are observed. For x = 0.40, a susceptibility
hump is seen at 30 K, suggesting the onset of static AF order. A magnetic jump,
which is likely to be triggered by charge ordering, is clearly observed at Tt =
175 K in samples with x = 0.50 (= 1/2) and 0.67 (= 2/3), while only a tiny kink
appears at T = 210 K in the sample with an intermediate Li composition, x =
0.60. Thus, the phase diagram of the LixCoO2 system is complex, and the
electronic properties are sensitively influenced by the Li content (x).Comment: 29 pages, 1 table, 9 figure
Compatibility of localized wave packets and unrestricted single particle dynamics for cluster formation in nuclear collisions
Antisymmetrized molecular dynamics with quantum branching is generalized so
as to allow finite time duration of the unrestricted coherent mean field
propagation which is followed by the decoherence into wave packets. In this new
model, the wave packet shrinking by the mean field propagation is respected as
well as the diffusion, so that it predicts a one-body dynamics similar to that
in mean field models. The shrinking effect is expected to change the diffusion
property of nucleons in nuclear matter and the global one-body dynamics. The
central \xenon+\tin collisions at 50 MeV/nucleon are calculated by the models
with and without shrinking, and it is shown that the inclusion of the wave
packet shrinking has a large effect on the multifragmentation in a big
expanding system with a moderate expansion velocity.Comment: 16 pages, 7 figure
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