368 research outputs found
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
The High Magnetic Field Phase Diagram of a Quasi-One Dimensional Metal
We present a unique high magnetic field phase of the quasi-one dimensional
organic conductor (TMTSF)ClO. This phase, termed "Q-ClO", is
obtained by rapid thermal quenching to avoid ordering of the ClO anion. The
magnetic field dependent phase of Q-ClO is distinctly different from that
in the extensively studied annealed material. Q-ClO exhibits a spin density
wave (SDW) transition at 5 K which is strongly magnetic field
dependent. This dependence is well described by the theoretical treatment of
Bjelis and Maki. We show that Q-ClO provides a new B-T phase diagram in the
hierarchy of low-dimensional organic metals (one-dimensional towards
two-dimensional), and describe the temperature dependence of the of the quantum
oscillations observed in the SDW phase.Comment: 10 pages, 4 figures, preprin
Equilibrium magnetisation structures in ferromagnetic nanorings
The ground state of the ring-shape magnetic nanoparticle is studied.
Depending on the geometrical and magnetic parameters of the nanoring, there
exist different magnetisation configurations (magnetic phases): two phases with
homogeneous magnetisation (easy-axis and easy-plane phases) and two
inhomogeneous (planar vortex phase and out-of-plane one). The existence of a
new intermediate out-of-plane vortex phase, where the inner magnetisation is
not strongly parallel to the easy axis, is predicted. Possible transitions
between different phases are analysed using the combination of analytical
calculations and micromagnetic simulations.Comment: LaTeX, 19 pages, 11 figure
Spin-density-wave transition of (TMTSF)PF at high magnetic fields
The transverse magnetoresistance of the Bechgaard salt (TMTSF)PF has
been measured for various pressures, with the field up to 24 T parallel to the
lowest conductivity direction c. A quadratic behavior is observed in
the magnetic field dependence of the spin-density-wave (SDW) transition
temperature . With increasing pressure,
decreases and the coefficient of the quadratic term increases. These results
are consistent with the prediction of the mean-field theory based on the
nesting of the quasi one-dimensional Fermi surface. Using a mean field theory,
for the perfect nesting case is estimated as about 16 K. This
means that even at ambient pressure where is 12 K, the SDW
phase of (TMTSF)PF is substantially suppressed by the
two-dimensionality of the system.Comment: 11pages,6figures(EPS), accepted for publication in PR
Transport of Dirac quasiparticles in graphene: Hall and optical conductivities
The analytical expressions for both diagonal and off-diagonal ac and dc
conductivities of graphene placed in an external magnetic field are derived.
These conductivities exhibit rather unusual behavior as functions of frequency,
chemical potential and applied field which is caused by the fact that the
quasiparticle excitations in graphene are Dirac-like. One of the most striking
effects observed in graphene is the odd integer quantum Hall effect. We argue
that it is caused by the anomalous properties of the Dirac quasiparticles from
the lowest Landau level. Other quantities such as Hall angle and Nernst signal
also exhibit rather unusual behavior, in particular when there is an excitonic
gap in the spectrum of the Dirac quasiparticle excitations.Comment: 25 pages, RevTeX4, 8 EPS figures; final version published in PR
Isolation and regeneration of transiently transformed protoplasts from gametophytic blades of the marine red alga Porphyra yezoensis
Despite the recent progress of transient gene expression systems in a
red alga Porphyra yezoensis by particle bombardment, a stable
transformation system has yet to establish in any marine red
macrophytes. One of the reasons of the difficulty in genetic
transformation in red algae is the lack of systems to select and
isolate transformed cells from gametophytic blades. Thus, toward the
establishment of the stable transformation system in P. yezoensis, we
have developed a procedure by which transiently transformed
gametophytic cells were prepared from particle bombarded-gametophytic
blade as regeneratable protoplasts. Using mixture of marine bacterial
enzymes, yield of protoplasts was high as reported elsewhere; however,
these protoplasts did not develop. In contrast, protoplasts prepared
from gametophytes treated with allantoin were normally developed, in
which the overexpression of a \u3b2-glucuronidase reporter gene had no
effect on the regeneration of protoplasts. Therefore, the use of
allantoin in protoplast preparation sheds a new light on the
realization of an efficient isolation and selection of study
transformed cells from gametophytic blades
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