697 research outputs found
Stress Dependence of Exciton Relaxation Processes in Cu2O
A comprehensive study of the exciton relaxation processes in Cu2O has led to
some surprises. We find that the ortho-para conversion rate becomes slower at
high stress, and that the Auger nonradiative recombination rate increases with
stress, with apparently no Auger recombination at zero stress. These results
have important consequences for the pursuit of Bose-Einstein condensation of
excitons in a harmonic potential.Comment: 10 figures, 1 tabl
Strain engineering in graphene by laser irradiation
We demonstrate that the Raman spectrum of graphene on lithium niobate can be controlled locally by continuous exposure to laser irradiation. We interpret our results in terms of changes to doping and mechanical strain and show that our observations are consistent with light-induced gradual strain relaxation in the graphene layer
Tiling of the five-fold surface of Al(70)Pd(21)Mn(9)
The nature of the five-fold surface of Al(70)Pd(21)Mn(9) has been
investigated using scanning tunneling microscopy. From high resolution images
of the terraces, a tiling of the surface has been constructed using pentagonal
prototiles. This tiling matches the bulk model of Boudard et. al. (J. Phys.:
Cond. Matter 4, 10149, (1992)), which allows us to elucidate the atomic nature
of the surface. Furthermore, it is consistent with a Penrose tiling T^*((P1)r)
obtained from the geometric model based on the three-dimensional tiling
T^*(2F). The results provide direct confirmation that the five-fold surface of
i-Al-Pd-Mn is a termination of the bulk structure.Comment: 4 pages, 4 figure
The instability of Alexander-McTague crystals and its implication for nucleation
We show that the argument of Alexander and McTague, that the bcc crystalline
structure is favored in those crystallization processes where the first order
character is not too pronounced, is not correct. We find that any solution that
satisfies the Alexander-McTague condition is not stable. We investigate the
implication of this result for nucleation near the pseudo- spinodal in
near-meanfield systems.Comment: 20 pages, 0 figures, submitted to Physical Review
Cut Points and Diffusions in Random Environment
In this article we investigate the asymptotic behavior of a new class of
multi-dimensional diffusions in random environment. We introduce cut times in
the spirit of the work done by Bolthausen, Sznitman and Zeitouni, see [4], in
the discrete setting providing a decoupling effect in the process. This allows
us to take advantage of an ergodic structure to derive a strong law of large
numbers with possibly vanishing limiting velocity and a central limit theorem
under the quenched measure.Comment: 44 pages; accepted for publication in "Journal of Theoretical
Probability
Constraints on cosmic hemispherical power anomalies from quasars
Recent analyses of the cosmic microwave background (CMB) maps from the WMAP
satellite have uncovered evidence for a hemispherical power anomaly, i.e. a
dipole modulation of the CMB power spectrum at large angular scales with an
amplitude of +/-14 percent. Erickcek et al have put forward an inflationary
model to explain this anomaly. Their scenario is a variation on the curvaton
scenario in which the curvaton possesses a large-scale spatial gradient that
modulates the amplitude of CMB fluctuations. We show that this scenario would
also lead to a spatial gradient in the amplitude of perturbations sigma_8, and
hence to a dipole asymmetry in any highly biased tracer of the underlying
density field. Using the high-redshift quasars from the Sloan Digital Sky
Survey, we find an upper limit on such a gradient of |nabla
sigma_8|/sigma_8<0.027/r_{lss} (99% posterior probability), where r_{lss} is
the comoving distance to the last-scattering surface. This rules out the
simplest version of the curvaton spatial gradient scenario.Comment: matches JCAP accepted version (minor revisions
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Momentum dependent dxz/yz band splitting in LaFeAsO
The nematic phase in iron based superconductors (IBSs) has attracted attention with a notion that it may provide important clue to the superconductivity. A series of angle-resolved photoemission spectroscopy (ARPES) studies were performed to understand the origin of the nematic phase. However, there is lack of ARPES study on LaFeAsO nematic phase. Here, we report the results of ARPES studies of the nematic phase in LaFeAsO. Degeneracy breaking between the dxz and dyz hole bands near the Γ and M point is observed in the nematic phase. Different temperature dependent band splitting behaviors are observed at the Γ and M points. The energy of the band splitting near the M point decreases as the temperature decreases while it has little temperature dependence near the Γ point. The nematic nature of the band shift near the M point is confirmed through a detwin experiment using a piezo device. Since a momentum dependent splitting behavior has been observed in other iron based superconductors, our observation confirms that the behavior is a universal one among iron based superconductors
Doping-insensitive density-of-states suppression in polycrystalline iron-based superconductor SmOFFeAs
We investigated the temperature dependence of the density-of-states in the
iron-based superconductor SmO_1-xF_xFeAs (x=0, 0.12, 0.15, 0.2) with high
resolution angle-integrated photoemission spectroscopy. The density-of-states
suppression is observed with decreasing temperature in all samples, revealing
two characteristic energy scales (10meV and 80meV). However, no obvious doping
dependence is observed. We argue that the 10meV suppression is due to an
anomalously doping-independent normal state pseudogap, which becomes the
superconducting gap once in the superconducting state; and alert the
possibility that the 80meV-scale suppression might be an artifact of the
polycrystalline samples.Comment: 4 pages, 4 figure
Structural aspects of the fivefold quasicrystalline Al–Cu–Fe surface from STM and dynamical LEED studies
Quantifying atmospheric nitrogen deposition through a nationwide monitoring network across China
A Nationwide Nitrogen Deposition Monitoring Network (NNDMN) containing 43 monitoring sites was established in China to measure gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3− in air and/or precipitation from 2010 to 2014. Wet/bulk deposition fluxes of Nr species were collected by precipitation gauge method and measured by continuous-flow analyzer; dry deposition fluxes were estimated using airborne concentration measurements and inferential models. Our observations reveal large spatial variations of atmospheric Nr concentrations and dry and wet/bulk Nr deposition. On a national basis, the annual average concentrations (1.3–47.0 μg N m−3) and dry plus wet/bulk deposition fluxes (2.9–83.3 kg N ha−1 yr−1) of inorganic Nr species are ranked by land use as urban > rural > background sites and by regions as north China > southeast China > southwest China > northeast China > northwest China > Tibetan Plateau, reflecting the impact of anthropogenic Nr emission. Average dry and wet/bulk N deposition fluxes were 20.6 ± 11.2 (mean ± standard deviation) and 19.3 ± 9.2 kg N ha−1 yr−1 across China, with reduced N deposition dominating both dry and wet/bulk deposition. Our results suggest atmospheric dry N deposition is equally important to wet/bulk N deposition at the national scale. Therefore, both deposition forms should be included when considering the impacts of N deposition on environment and ecosystem health
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