3,375 research outputs found
Field-induced magnetic ordering in the Haldane system PbNi2V2O8
The Haldane system PbNi2V2O8 was investigated by the temperature dependent
magnetization M(T) measurements at fields higher than H_c, with H_c the
critical fields necessary to close the Haldane gap. It is revealed that M(T)
for H > H_c exhibits a cusp-like minimum at T_{min}, below which M(T) increases
with decreasing T having a convex curve. These features have been observed for
both and , with c-axis being parallel to the chain.
These data indicate the occurrence of field-induced magnetic ordering around
T_{min}. Phase boundaries for and do not cross each
other, consistent with the theoretical calculation for negative single-ion
anisotropy D.Comment: 3 figures, submitted to Phys. Rev.
Single crystal MgB2 with anisotropic superconducting properties
The discovery of superconductor in magnesium diboride MgB2 with high Tc (39
K) has raised some challenging issues; whether this new superconductor
resembles a high temperature cuprate superconductor(HTS) or a low temperature
metallic superconductor; which superconducting mechanism, a phonon- mediated
BCS or a hole superconducting mechanism or other new exotic mechanism may
account for this superconductivity; and how about its future for applications.
In order to clarify the above questions, experiments using the single crystal
sample are urgently required. Here we have first succeeded in obtaining the
single crystal of this new MgB2 superconductivity, and performed its electrical
resistance and magnetization measurements. Their experiments show that the
electronic and magnetic properties depend on the crystallographic direction.
Our results indicate that the single crystal MgB2 superconductor shows
anisotropic superconducting properties and thus can provide scientific basis
for the research of its superconducting mechanism and its applications.Comment: 7 pages pdf fil
Designing molecules to bypass the singlet-triplet bottleneck in the electroluminescence of organic light-emitting-diode materials
Electroluminescence in organic light emitting diode (OLED) materials occurs
via the recombination of excitonic electrons-hole pairs Only the singlet
excitons of commonly used OLED materials, e.g., Aluminum trihydroxyquinoline
(AlQ), decay radiatively, limiting the external quantum efficiency to a
maximum 25%. Thus 75% of the energy is lost due to the triplet bottleneck for
radiative recombination. We consider molecules derived from AlQ which
bypass the triplet bottleneck by designing structures which contain strong
spin-orbit coupling. As a first stage of this work, groundstate energies and
vertical excitation energies of Al-arsenoquinolines and Al-boroarsenoquinolines
are calculated. It is found that the substitution of N by As leads to very
favourable results, while the boron substitution leads to no advantage.Comment: 4 pages, 4 figue
Magnetic phase diagram of antiferroquadrupole ordering in HoB2C2
The magnetic phase diagram for antiferro-quadrupole (AFQ) ordering in
tetragonal HoBC has been investigated by measurements of elastic
constants , and in fields along the basal -
plane as well as the principal [001]-axis. The hybrid magnet (GAMA) in Tsukuba
Magnetic Laboratory was employed for high field measurements up to 30 T. The
AFQ phase is no longer observed above 26.3 T along the principal [001] axis in
contrast to the relatively small critical field of 3.9 T in fields applied
along the basal [110] axis. The quadrupolar intersite interaction of
and/or is consistent with the anisotropy in the magnetic phase diagram
of the AFQ phase in HoBC.Comment: Phys. Rev. B. (2005) in press. approx 8 pages, 10 figure
A non-perturbative approach to halo breakup
The theory of weakly bound cluster breakup, like halo nucleus breakup, needs
an accurate treatment of the transitions from bound to continuum states induced
by the nuclear and Coulomb potentials. When the transition probability is not
very small, a non-perturbative framework might be necessary. Nuclear excitation
dominates at small impact parameters whereas the Coulomb potential being long
range acts over a larger impact parameter interval. In this article, we propose
an effective breakup amplitude which meets a number of requirements necessary
for an accurate quantitative description of the breakup reaction mechanism.
Furthermore our treatment gives some insight on the interplay between time
dependent perturbation theory and sudden approximation and it allows to include
the nuclear and Coulomb potentials to all orders within an eikonal-like
framework.Comment: 22 Latex pages, 1 table, 8 eps figures. Accepted for publication on
Nucl. Phys.
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