1,194 research outputs found
Angular dependent magnetothermopower of α-(ET)₂KHg(SCN)₄
The magnetic field and angular dependences of the thermopower and Nernst effect of the quasi-twodimensional (q2D) organic conductor α-(ET)₂KHg(SCN)₄ are experimentally measured at temperatures below (4 K) and above (9 K) the transition temperature to fields of 31 T. In addition, a theoretical model which involves a magnetic breakdown effect between the q1D and q2D bands is proposed in order to simulate the data. Analysis of the background components of the thermopower and Nernst effect imply that at low temperatures, in the CDW state, the properties of α-(ET)₂KHg(SCN)₄ are determined mostly by the orbits on the new open Fermi sheets. Quantum oscillations observed in the both thermoelectric effects, at fields above 8 T, originate only from the α orbit
Role of anion size, magnetic moment, and disorder on the properties of the organic conductor kappa-(BETS)_2Ga_{1-x}Fe_{x}Cl_{4-y}_Br_{y}
Shubnikov-de Haas and angular dependent magnetoresistance oscillations have
been used to explore the role of anion size, magnetic moment, and disorder in
the organic conductors kappa-(BETS)_2GaBr_{4} and kappa-(BETS)_2FeCl_{2}_Br_{2}
in the isomorphic class kappa-(BETS)_2Ga_{1-x}Fe_{x}Cl_{4-y}_Br_{y}. The
results, combined with previous work, show correlations between the anion
composition (Ga_{1-x}Fe_{x}Cl_{4-y}_Br_{y}) and the superconducting transition
temperature, effective mass, Fermi surface topology, and the mean free path.Comment: 5 pages, 6 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
Magnetic Field Dependent Behavior of the CDW ground state in Per2M(mnt)2 (M = Au, Pt)
The Per2M(mnt)2 class of organic conductors exhibit a charge density wave
(CDW) ground state below about 12 K, which may be suppressed in magnetic fields
of order 20 to 30 T. However, for both cases of counter ion M(mnt)2 species
studied (M = Au (zero spin) and M = Pt (spin 1/2)), new high field ground
states evolve for further increases in magnetic field. We report recent
investigations where thermopower, Hall effect, high pressure and additional
transport measurements have been carried out to explore these new high field
phases.Comment: 6 pages, 10 figures, 27 reference
Effectiveness of the global protected area network in representing species diversity
The Fifth World Parks Congress in Durban, South Africa, announced in September 2003 that the global network of protected areas now covers 11.5% of the planet's land surface. This surpasses the 10% target proposed a decade earlier, at the Caracas Congress, for 9 out of 14 major terrestrial biomes. Such uniform targets based on percentage of area have become deeply embedded into national and international conservation planning. Although politically expedient, the scientific basis and conservation value of these targets have been questioned. In practice, however, little is known of how to set appropriate targets, or of the extent to which the current global protected area network fulfils its goal of protecting biodiversity. Here, we combine five global data sets on the distribution of species and protected areas to provide the first global gap analysis assessing the effectiveness of protected areas in representing species diversity. We show that the global network is far from complete, and demonstrate the inadequacy of uniform—that is, 'one size fits all'—conservation targets
A search for ionized jets towards massive young stellar objects
Radio continuum observations using the Australia telescope compact array at 5.5, 9.0, 17.0 and 22.8 GHz have detected free-free emission associated with 45 of 49 massive young stellar objects and H II regions. Of these, 26 sources are classified as ionized jets (12 of which are candidates), 2 as ambiguous jets or disc winds, 1 as a disc-wind, 14 as H II regions and 2 were unable to be categorized. Classification as ionized jets is based upon morphology, radio flux and spectral index, in conjunction with previous observational results at other wavelengths. Radio luminosity and momentum are found to scale with bolometric luminosity in the same way as low-mass jets, indicating a common mechanism for jet production across all masses. In 13 of the jets, we see associated non-thermal/optically thin lobes resulting from shocks either internal to the jet and/or at working surfaces. 10 jets display non-thermal (synchrotron emission) spectra in their lobes, with an average spectral index of ? =-0.55 consistent with Fermi acceleration in shocks. This shows that magnetic fields are present, in agreement with models of jet formation incorporatingmagnetic fields. Since the production of collimated radio jets is associated with accretion processes, the results presented in this paper support the picture of disc-mediated accretion for the formation of massive stars with an upper limit on the jet phase lasting approximately 6.5×104 yr. Typical mass-loss rates in the jet are found to be 1.4× 10-5M? yr-1 with associated momentum rates of the order of (1-2) × 10-2M? km s-1 yr-1. © 2016 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society
Magnetothemopower study of quasi two-dimensional organic conductor -(BEDT-TTF)KHg(SCN)
We have used a low-frequency magneto-thermopower (MTEP) method to probe the
high magnetic field ground state behavior of
-(BEDT-TTF)KHg(SCN) along all three principal crystallographic
axes at low temperatures. The thermopower tensor coefficients (
and ) have been measured to 30 T, beyond the anomalous low temperature,
field-induced transition at 22.5 T. We find a significant anisotropy in the
MTEP signal, and also observe large quantum oscillations associated with the de
Haas - van Alphen effect. The anisotropy indicates that the ground state
properties are clearly driven by mechanisms that occur along specific
directions for the in-plane electronic structure. Both transverse and
longitudinal magnetothermopower show asymptotic behavior in field, which can be
explained in terms of magnetic breakdown of compensated closed orbits.Comment: 9 pages, 10 figure
Periodic orbit resonances in layered metals in tilted magnetic fields
The frequency dependence of the interlayer conductivity of a layered Fermi
liquid in a magnetic field which is tilted away from the normal to the layers
is considered. For both quasi-one- and quasi-two-dimensional systems resonances
occur when the frequency is a harmonic of the frequency at which the magnetic
field causes the electrons to oscillate on the Fermi surface within the layers.
The intensity of the different harmonic resonances varies significantly with
the direction of the field. The resonances occur for both coherent and weakly
incoherent interlayer transport and so their observation does not imply the
existence of a three-dimensional Fermi surface.Comment: 4 pages, RevTeX + epsf, 2 figures. Discussion of other work revised.
To appear in Phys. Rev. B, Rapid Commun., October 1
The Frequency Dependence of Critical-velocity Behavior in Oscillatory Flow of Superfluid Helium-4 Through a 2-micrometer by 2-micrometer Aperture in a Thin Foil
The critical-velocity behavior of oscillatory superfluid Helium-4 flow
through a 2-micrometer by 2-micrometer aperture in a 0.1-micrometer-thick foil
has been studied from 0.36 K to 2.10 K at frequencies from less than 50 Hz up
to above 1880 Hz. The pressure remained less than 0.5 bar. In early runs during
which the frequency remained below 400 Hz, the critical velocity was a
nearly-linearly decreasing function of increasing temperature throughout the
region of temperature studied. In runs at the lowest frequencies, isolated 2 Pi
phase slips could be observed at the onset of dissipation. In runs with
frequencies higher than 400 Hz, downward curvature was observed in the decrease
of critical velocity with increasing temperature. In addition, above 500 Hz an
alteration in supercritical behavior was seen at the lower temperatures,
involving the appearance of large energy-loss events. These irregular events
typically lasted a few tens of half-cycles of oscillation and could involve
hundreds of times more energy loss than would have occurred in a single
complete 2 Pi phase slip at maximum flow. The temperatures at which this
altered behavior was observed rose with frequency, from ~ 0.6 K and below, at
500 Hz, to ~ 1.0 K and below, at 1880 Hz.Comment: 35 pages, 13 figures, prequel to cond-mat/050203
Magnetism and electron spin resonance in single crystalline beta-AgNpO2(SeO3)
We report magnetization, susceptibility, electrical transport, and electron
spin resonance (ESR) studies of single crystals of beta-AgNpO2(SeO3). Here the
valence of the Np sites is expected to be Np(V). We observe a magnetic
transition below 8 K, where the transition temperature is dependent on the
effective magnetic moment. Although the transition appears to be ferromagnetic,
no hysteresis is seen in the magnetization, and the saturation moment above 0.1
T is found to be about 60% of the free NpO2 ion moment. The decrease in the Np
moments determined experimentally is thought to arise from crystal field and
spin-orbit effects. Although Np(V) is expected to be ESR silent, we observe
temperature dependent ESR spectra at ~44 GHz (for fields above the saturation
field) that show slight shifts in the g-factor and line width at low
temperatures. Our results provide evidence that both Np(V) and Np(IV) valences
are present, where the latter may be a minority population. The crystals,
although dark in appearance, are electrically insulating (rho > 10^10 Ohm-cm)
at room temperature.Comment: 6 pages, 8 figure
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