22,953 research outputs found
Unifying Description of Competing Orders in Two Dimensional Quantum Magnets
Quantum magnets provide the simplest example of strongly interacting quantum
matter, yet they continue to resist a comprehensive understanding above one
spatial dimension (1D). In 1D, a key ingredient to progress is Luttinger liquid
theory which provides a unified description. Here we explore a promising
analogous framework in two dimensions, the Dirac spin liquid (DSL), which can
be constructed on several different lattices. The DSL is a version of Quantum
Electrodynamics ( QED) with four flavors of Dirac fermions coupled to
photons. Importantly, its excitations also include magnetic monopoles that
drive confinement. By calculating the complete action of symmetries on
monopoles on the square, honeycomb, triangular and kagom\`e lattices, we answer
previously open key questions. We find that the stability of the DSL is
enhanced on the triangular and kagom\`e lattices as compared to the bipartite
(square and honeycomb) lattices. We obtain the universal signatures of the DSL
on the triangular and kagom\`e lattices, including those that result from
monopole excitations, which serve as a guide to numerics and to experiments on
existing materials. Interestingly, the familiar 120 degree magnetic orders on
these lattices can be obtained from monopole proliferation. Even when unstable,
the Dirac spin liquid unifies multiple ordered states which could help organize
the plethora of phases observed in strongly correlated two-dimensional
materials.Comment: 13+9 pages, 7 figure
Exploring the total Galactic extinction with SDSS BHB stars
Aims: We used 12,530 photometrically-selected blue horizontal branch (BHB)
stars from the Sloan Digital Sky Survey (SDSS) to estimate the total extinction
of the Milky Way at the high Galactic latitudes, and in each line
of sight. Methods: A Bayesian method was developed to estimate the reddening
values in the given lines of sight. Based on the most likely values of
reddening in multiple colors, we were able to derive the values of and
.
Results: We selected 94 zero-reddened BHB stars from seven globular clusters
as the template. The reddening in the four SDSS colors for the northern
Galactic cap were estimated by comparing the field BHB stars with the template
stars. The accuracy of this estimation is around 0.01\,mag for most lines of
sight. We also obtained to be around 2.40 and map within
an uncertainty of 0.1\,mag. The results, including reddening values in the four
SDSS colors, , and in each line of sight, are released on line. In
this work, we employ an up-to-date parallel technique on GPU card to overcome
time-consuming computations. We plan to release online the C++ CUDA code used
for this analysis.
Conclusions: The extinction map derived from BHB stars is highly consistent
with that from Schlegel, Finkbeiner & Davis(1998). The derived is around
2.40. The contamination probably makes the be larger.Comment: 16 pages, 13 figures, 4 tables, accepted for publication in A&
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