13,482 research outputs found
Duality picture between antiferromagnetism and d-wave superconductivity in t-J model at two dimensions
We show in this paper an interesting relation between elementary and
topological excitations in the antiferromagnetic and d-wave superconducting
phases of the t-J model at two dimenions. The topological spin and charge
excitations in one phase have the same dynamics as elementary excitations in
the other phase, except the appearance of energy gaps. Moreover, the transition
from one phase to another can be described as a quantum disordering transition
associated with the topological excitations. Based on the above picture, a
plausible phase diagram of t-J model is constructed.Comment: 28 pages, 3 figure
CO2 perturbation experiments: similarities and differences between dissolved inorganic carbon and total alkalinity manipulations
Increasing atmospheric carbon dioxide (CO2) through human activities and invasion of anthropogenic CO2 into the surface ocean alters the seawater carbonate chemistry, increasing CO2 and bicarbonate (HCO3−) at the expense of carbonate ion (CO32−) concentrations. This redistribution in the dissolved inorganic carbon (DIC) pool decreases pH and carbonate saturation state (Ω). Several components of the carbonate system are considered potential key variables influencing for instance calcium carbonate precipitation in marine calcifiers such as coccolithophores, foraminifera, corals, mollusks and echinoderms. Unravelling the sensitivities of marine organisms and ecosystems to CO2 induced ocean acidification (OA) requires well-controlled experimental setups and accurate carbonate system manipulations. Here we describe and analyse the chemical changes involved in the two basic approaches for carbonate chemistry manipulation, i.e. changing DIC at constant total alkalinity (TA) and changing TA at constant DIC. Furthermore, we briefly introduce several methods to experimentally manipulate DIC and TA. Finally, we examine responses obtained with both approaches using published results for the coccolithophore Emiliania huxleyi. We conclude that under most experimental conditions in the context of ocean acidification DIC and TA manipulations yield similar changes in all parameters of the carbonate system, which implies direct comparability of data obtained with the two basic approaches for CO2 perturbation
Time-Reversal Symmetry Breaking and Spontaneous Anomalous Hall Effect in Fermi Fluids
We study the spontaneous non-magnetic time-reversal symmetry breaking in a
two-dimensional Fermi liquid without breaking either the translation symmetry
or the U(1) charge symmetry. Assuming that the low-energy physics is described
by fermionic quasiparticle excitations, we identified an "emergent" local
symmetry in momentum space for an -band model. For a large class of
models, including all one-band and two-band models, we found that the
time-reversal and chiral symmetry breaking can be described by the
gauge theory associated with this emergent local symmetry. This
conclusion enables the classification of the time-reversal symmetry-breaking
states as types I and II, depending on the type of accompanying spatial
symmetry breaking. The properties of each class are studied. In particular, we
show that the states breaking both time-reversal and chiral symmetries are
described by spontaneously generated Berry phases. We also show examples of the
time-reversal symmetry-breaking phases in several different microscopically
motivated models and calculate their associated Hall conductance within a
mean-field approximation. The fermionic nematic phase with time-reversal
symmetry breaking is also presented and the possible realizations in strongly
correlated models such as the Emery model are discussed.Comment: 18 pages, 8 figure
Biases in metallicity measurements from global galaxy spectra: the effects of flux-weighting and diffuse ionized gas contamination
Galaxy metallicity scaling relations provide a powerful tool for
understanding galaxy evolution, but obtaining unbiased global galaxy gas-phase
oxygen abundances requires proper treatment of the various line-emitting
sources within spectroscopic apertures. We present a model framework that
treats galaxies as ensembles of HII and diffuse ionized gas (DIG) regions of
varying metallicities. These models are based upon empirical relations between
line ratios and electron temperature for HII regions, and DIG strong-line ratio
relations from SDSS-IV MaNGA IFU data. Flux-weighting effects and DIG
contamination can significantly affect properties inferred from global galaxy
spectra, biasing metallicity estimates by more than 0.3 dex in some cases. We
use observationally-motivated inputs to construct a model matched to typical
local star-forming galaxies, and quantify the biases in strong-line ratios,
electron temperatures, and direct-method metallicities as inferred from global
galaxy spectra relative to the median values of the HII region distributions in
each galaxy. We also provide a generalized set of models that can be applied to
individual galaxies or galaxy samples in atypical regions of parameter space.
We use these models to correct for the effects of flux-weighting and DIG
contamination in the local direct-method mass-metallicity and fundamental
metallicity relations, and in the mass-metallicity relation based on
strong-line metallicities. Future photoionization models of galaxy line
emission need to include DIG emission and represent galaxies as ensembles of
emitting regions with varying metallicity, instead of as single HII regions
with effective properties, in order to obtain unbiased estimates of key
underlying physical properties.Comment: 37 pages, 29 figures, 4 tables. Accepted to ApJ. See Figures 15-17
for typical global galaxy biases in strong-line ratios, electron
temperatures, and direct-method metallicitie
Shot noise in magnetic tunnel junctions from first principles
We compute the shot noise in ballistic and disordered Fe/MgO/Fe tunnel
junctions by a wave function-matching method. For tunnel barriers with no more
than 5 atomic layers we find a suppression of the Fano factor as a function of
the magnetic configuration. For thicker MgO barriers the shot noise is
suppressed up to a threshold bias indicating the onset of resonant tunneling.
We find excellent agreement with recent experiments when interface disorder is
taken into accountComment: 5 pages,5 figure
[N]pT ensemble and finite-size scaling study of the GEM-4 critical isostructural transition
First-order transitions of system where both lattice site occupancy and
lattice spacing fluctuate, such as cluster crystals, cannot be efficiently
studied by traditional simulation methods. These methods necessarily fix one of
these two degrees of freedom, but this difficulty is surmounted by the
generalized [N]pT ensemble [J. Chem. Phys. 136, 214106 (2012)]. Here it is
shown that histogram reweighting and the [N]pT ensemble can be used to study an
isostructural transition between cluster crystals of different occupancy in the
generalized exponential model of index 4 (GEM-4). Extending this scheme to
finite-size scaling studies also allows to accurately determine the critical
point parameters and to verify that it belongs to the Ising universality class.Comment: 5 pages, 4 figure
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