4,164 research outputs found
Mott Gap Excitations and Resonant Inelastic X-Ray Scattering in Doped Cuprates
Predictions are made for the momentum- and carrier-dependent degradation of
the Mott gap upon doping in high-Tc cuprates as would be observed in Cu K-edge
resonant inelastic x-ray scattering (RIXS). The two-dimensional Hubbard model
with second- and third-nearest-neighbor hopping terms has been studied by
numerical exact diagonalization. Special emphasis is placed on the
particle-hole asymmetry of the Mott gap excitations. We argue that the Mott gap
excitations observed by RIXS are significantly influenced by the interaction
between charge carriers and antiferromagnetic correlations.Comment: 4 pages, 4 figures, revised version; to be published in Phys. Rev.
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Reliable postprocessing improvement of van der Waals heterostructures
The successful assembly of heterostructures consisting of several layers of
different 2D materials in arbitrary order by exploiting van der Waals forces
has truly been a game changer in the field of low dimensional physics. For
instance, the encapsulation of graphene or MoS2 between atomically flat
hexagonal boron nitride (hBN) layers with strong affinity and graphitic gates
that screen charge impurity disorder provided access to a plethora of
interesting physical phenomena by drastically boosting the device quality. The
encapsulation is accompanied by a self-cleansing effect at the interfaces. The
otherwise predominant charged impurity disorder is minimized and random strain
fluctuations ultimately constitute the main source of residual disorder.
Despite these advances, the fabricated heterostructures still vary notably in
their performance. While some achieve record mobilities, others only possess
mediocre quality. Here, we report a reliable method to improve fully completed
van der Waals heterostructure devices with a straightforward post-processing
surface treatment based on thermal annealing and contact mode AFM. The impact
is demonstrated by comparing magnetotransport measurements before and after the
AFM treatment on one and the same device as well as on a larger set of treated
and untreated devices to collect device statistics. Both the low temperature
properties as well as the room temperature electrical characteristics, as
relevant for applications, improve on average substantially. We surmise that
the main beneficial effect arises from reducing nanometer scale corrugations at
the interfaces, i.e. the detrimental impact of random strain fluctuations
Impact of dark matter subhalos on extended HI disks of galaxies: Possible formation of HI fine structures and stars
Recent observations have discovered star formation activities in the extreme
outer regions of disk galaxies. However it remains unclear what physical
mechanisms are responsible for triggering star formation in such low-density
gaseous environments of galaxies. In order to understand the origin of these
outer star-forming regions, we numerically investigate how the impact of dark
matter subhalos orbiting a gas-rich disk galaxy embedded in a massive dark
matter halo influences the dynamical evolution of outer HI gas disk of the
galaxy. We find that if the masses of the subhalos () in a galaxy
with an extended HI gas disk are as large as , where
is the total mass of the galaxy's dark halo, local fine structures
can be formed in the extended HI disk. We also find that the gas densities of
some apparently filamentary structures can exceed a threshold gas density for
star formation and thus be likely to be converted into new stars in the outer
part of the HI disk in some models with larger . These results thus
imply that the impact of dark matter subhalos (``dark impact'') can be
important for better understanding the origin of recent star formation
discovered in the extreme outer regions of disk galaxies. We also suggest that
characteristic morphologies of local gaseous structures formed by the dark
impact can indirectly prove the existence of dark matter subhalos in galaxies.
We discuss the origin of giant HI holes observed in some gas-rich galaxies
(e.g., NGC 6822) in the context of the dark impact.Comment: 8 pages, 4 figures, accepted by ApJ
Mass Shift and Width Broadening of J/psi in hot gluonic plasma from QCD Sum Rules
We investigate possible mass shift and width broadening of J/psi in hot
gluonic matter using QCD sum rule. Input values of gluon condensates at finite
temperature are extracted from lattice QCD data for the energy density and
pressure. Although stability of the moment ratio is achieved only up to T/Tc ~
1.05, the gluon condensates cause a decrease of the moment ratio, which results
in change of spectral properties. Using the Breit-Wigner form for the
phenomenological side, we find that mass shift of J/psi just above Tc can reach
maximally 200 MeV and width can broaden to dozens of MeV.Comment: 4 pages, 5 figures, version to appear in Physical Review Letter
Even denominator fractional quantum Hall states in higher Landau levels of graphene
An important development in the field of the fractional quantum Hall effect
has been the proposal that the 5/2 state observed in the Landau level with
orbital index of two dimensional electrons in a GaAs quantum well
originates from a chiral -wave paired state of composite fermions which are
topological bound states of electrons and quantized vortices. This state is
theoretically described by a "Pfaffian" wave function or its hole partner
called the anti-Pfaffian, whose excitations are neither fermions nor bosons but
Majorana quasiparticles obeying non-Abelian braid statistics. This has inspired
ideas on fault-tolerant topological quantum computation and has also instigated
a search for other states with exotic quasiparticles. Here we report
experiments on monolayer graphene that show clear evidence for unexpected
even-denominator fractional quantum Hall physics in the Landau level. We
numerically investigate the known candidate states for the even-denominator
fractional quantum Hall effect, including the Pfaffian, the particle-hole
symmetric Pfaffian, and the 221-parton states, and conclude that, among these,
the 221-parton appears a potentially suitable candidate to describe the
experimentally observed state. Like the Pfaffian, this state is believed to
harbour quasi-particles with non-Abelian braid statistic
Validation of a novel scoring system for changes in skeletal manifestations of hypophosphatasia in newborns, infants, and children: The Radiographic Global Impression of Change scale
Hypophosphatasia (HPP) is the heritable metabolic disease characterized by impaired skeletal mineralization due to low activity of the tissue-nonspecific isoenzyme of alkaline phosphatase. Although HPP during growth often manifests with distinctive radiographic skeletal features, no validated method was available to quantify them, including changes over time. We created the Radiographic Global Impression of Change (RGI-C) scale to assess changes in the skeletal burden of pediatric HPP. Site-specific pairs of radiographs of newborns, infants, and children with HPP from three clinical studies of asfotase alfa, an enzyme replacement therapy for HPP, were obtained at baseline and during treatment. Each pair was scored by three pediatric radiologists ( raters ), with nine raters across the three studies. Intrarater and interrater agreement was determined by weighted Kappa coefficients. Interrater reliability was assessed using intraclass correlation coefficients (ICCs) and by two-way random effects analysis of variance (ANOVA) and a mixed-model repeated measures ANOVA. Pearson correlation coefficients evaluated relationships of the RGI-C to the Rickets Severity Scale (RSS), Pediatric Outcomes Data Collection Instrument Global Function Parent Normative Score, Childhood Health Assessment Questionnaire Disability Index, 6-Minute Walk Test percent predicted, and Z-score for height in patients aged 6 to 12 years at baseline. Eighty-nine percent (8/9) of raters showed substantial or almost perfect intrarater agreement of sequential RGI-C scores (weighted Kappa coefficients, 0.72 to 0.93) and moderate or substantial interrater agreement (weighted Kappa coefficients, 0.53 to 0.71) in patients aged 0 to 12 years at baseline. Moderate-to-good interrater reliability was observed (ICC, 0.57 to 0.65). RGI-C scores were significantly (p ≤ 0.0065) correlated with the RSS and with measures of global function, disability, endurance, and growth in the patients aged 6 to 12 years at baseline. Thus, the RGI-C is valid and reliable for detecting clinically important changes in skeletal manifestations of severe HPP in newborns, infants, and children, including during asfotase alfa treatment. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc
Sigma meson in QCD sum rules using a two quark current with derivatives
We study the meson in QCD sum rules using a two quark interpolating
field with derivatives. In the constituent quark model, the meson is
composed of a quark and an antiquark in the relative p-wave state and is thus
expected to have a larger overlap with an interpolating field that measures the
derivative of the relative quark wave-function. While the sum rule with a
current without derivatives gives a pole mass of around 1 GeV, the present sum
rule with a derivative current gives a mass of around 550 MeV and a width of
400 MeV, that could be identified with the meson.Comment: 4 pages, 2 figure
Critical behavior of charmonia across the phase transition: A QCD sum rule approach
We investigate medium-induced change of mass and width of J/psi and eta_c
across the phase transition in hot gluonic matter using QCD sum rules. In the
QCD sum rule approach, the medium effect on heavy quarkonia is induced by the
change of both scalar and twist-2 gluon condensates, whose temperature
dependences are extracted from the lattice calculations of energy density and
pressure. Although the stability of the operator product expansion side seems
to break down at T > 1.06Tc for the vector channel and T>1.04Tc for the
pseudoscalar channel, we find a sudden change of the spectral property across
the critical temperature Tc, which originates from an equally rapid change of
the scalar gluon condensate characterized by e-3p. By parameterizing the ground
state of the spectral density by the Breit-Wigner form, we find that for both
J/psi and eta_c, the masses suddenly decrease maximally by a few hundreds of
MeV and the widths broaden to ~100 MeV slightly above Tc. Implications for
recent and future heavy ion experiments are discussed.
We also carry out a similar analysis for charmonia in nuclear matter, which
could serve as a testing ground for observing the precursor phenomena of the
QCD phase transition. We finally discuss the possibility of observing the mass
shift at nuclear matter at the FAIR project at GSI.Comment: 18 pages, 21 figures, 2 figures are added and discussion on effect of
dynamical quarks is extended. version to appear in Phys.Rev.
The Galactic globular cluster system as a fossil record of reionization
We propose that structural, kinematical, and chemical properties of the
Galactic globular clusters (GCs) can contain fossil information of the cosmic
reionization history. We first summarize possible observational evidences for
the influence of reionization on the Galactic GC formation. We then show how
structural properties of the GC system (GCS) in the Galaxy can be influenced by
suppression of GC formation due to reionization during the Galaxy formation
through hierarchical merging of subgalactic clumps, by using numerical
simulations with and without suppression of GC formation by reionization. In
particular, we show that if GC formation in dwarf galaxies that are building
blocks of the Galaxy and virialized after reionization era () are
completely suppressed, the present-day radial distribution of the Galactic GCs
depends strongly on . Our numerical results imply that if GC
formation after 15 is strongly suppressed, the origin of the
observed structural properties of the Galactic GCS can be more naturally
explained in the framework of the hierarchical clustering scenario.Comment: 8 pages 3 figures (1 color jpg) ApJL in press (626, L93
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