14,695 research outputs found
Neutron Scattering Measurements of Spatially Anisotropic Magnetic Exchange Interactions in Semiconducting K0.85Fe1.54Se2 (TN=280 K)
We use neutron scattering to study the spin excitations associated with the
stripe antiferromagnetic (AFM) order in semiconducting
KFeSe (= K). We show that the spin wave spectra
can be accurately described by an effective Heisenberg Hamiltonian with highly
anisotropic in-plane couplings at = K. At high temperature (=
K) above , short range magnetic correlation with anisotropic correlation
lengths are observed. Our results suggest that, despite the dramatic difference
in the Fermi surface topology, the in-plane anisotropic magnetic couplings are
a fundamental property of the iron based compounds; this implies that their
antiferromagnetism may originate from local strong correlation effects rather
than weak coupling Fermi surface nesting.Comment: 5 pages, 4 figure
The Indonesian Throughflow Circulation Under Solar Geoengineering
The Indonesia Throughflow (ITF) is the only low-latitude channel between the Pacific and Indian oceans, and its variability has important effects on global climate and biogeochemical cycles. Climate models consistently predict a decline in ITF transport under global warming, but it has not yet been examined under solar geoengineering scenarios. We use standard parameterized methods for estimating ITF: the Amended Island Rule and Buoyancy Forcing, to investigate ITF under the SSP2-4.5 and SSP5-8.5 greenhouse gas scenarios, and the geoengineering experiments G6solar and G6sulfur that reduce net global mean radiative forcing from SSP5-8.5 levels to SSP2-4.5 levels using solar diming and sulfate aerosol injection strategies. Six model ensemble mean projections for 2080–2100 relative to historical ITF are reductions of 19 % under the G6solar scenario and 28 % under the G6sulfur scenario which compare with reductions of 23 % and 27 % under SSP2-4.5 and SSP5-8.5. Thus, significant weakening of the ITF occurs under all scenarios, but G6solar closer approximates SSP2-4.5 than does G6sulfur. In contrast with the other three scenarios which show only reductions in forcing due to ocean upwelling, the G6sulfur experiment shows a large reduction in ocean surface wind stress forcing accounting for 47 % (38 %~65 % across model range) of the decline of total ITF transport. There are also reductions in deep-sea upwelling in extratropical western boundary currents.</p
A novel mechanism of charge density wave in a transition metal dichalcogenide
Charge density wave, or CDW, is usually associated with Fermi surfaces
nesting. We here report a new CDW mechanism discovered in a 2H-structured
transition metal dichalcogenide, where the two essential ingredients of CDW are
realized in very anomalous ways due to the strong-coupling nature of the
electronic structure. Namely, the CDW gap is only partially open, and charge
density wavevector match is fulfilled through participation of states of the
large Fermi patch, while the straight FS sections have secondary or negligible
contributions.Comment: 5 pages and 4 figure
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Raman and Infra-red properties and layer dependence of the phonon dispersions in multi-layered graphene
The symmetry group analysis is applied to classify the phonon modes of
-stacked graphene layers (NSGL's) with AB- and AA-stacking, particularly
their infra-red and Raman properties. The dispersions of various phonon modes
are calculated in a multi-layer vibrational model, which is generalized from
the lattice vibrational potentials of graphene to including the inter-layer
interactions in NSGL's. The experimentally reported red shift phenomena in the
layer number dependence of the intra-layer optical C-C stretching mode
frequencies are interpreted. An interesting low frequency inter-layer optical
mode is revealed to be Raman or Infra-red active in even or odd NSGL's
respectively. Its frequency shift is sensitive to the layer number and
saturated at about 10 layers.Comment: enlarged versio
Evolution of the Electronic Structure of 1T-CuxTiSe2
The electronic structure of a new charge-density-wave/ superconductor system,
1T-CuxTiSe2, has been studied by photoemission spectroscopy. A correlated
semiconductor band structure is revealed for the undoped case. With Cu doping,
the charge density wave is suppressed by the raising of the chemical potential,
while the superconductivity is enhanced by the enhancement of the density of
states. Moreover, the strong scattering at high doping might be responsible for
the suppression of superconductivity in that regime.Comment: 5 pages, 4 figure
Inelastic X-Ray Scattering Study of Exciton Properties in an Organic Molecular crystal
Excitons in a complex organic molecular crystal were studied by inelastic
x-ray scattering (IXS) for the first time. The dynamic dielectric response
function is measured over a large momentum transfer region, from which an
exciton dispersion of 130 meV is observed. Semiempirical quantum chemical
calculations reproduce well the momentum dependence of the measured dynamic
dielectric responses, and thus unambiguously indicate that the lowest Frenkel
exciton is confined within a fraction of the complex molecule. Our results
demonstrate that IXS is a powerful tool for studying excitons in complex
organic molecular systems. Besides the energy position, the IXS spectra provide
a stringent test on the validity of the theoretically calculated exciton wave
functions.Comment: 4 pages, 4 figure
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