3,431 research outputs found
New Family of Robust 2D Topological Insulators in van der Waals Heterostructures
We predict a new family of robust two-dimensional (2D) topological insulators
in van der Waals heterostructures comprising graphene and chalcogenides BiTeX
(X=Cl, Br and I). The layered structures of both constituent materials produce
a naturally smooth interface that is conducive to proximity induced new
topological states. First principles calculations reveal intrinsic
topologically nontrivial bulk energy gaps as large as 70-80 meV, which can be
further enhanced up to 120 meV by compression. The strong spin-orbit coupling
in BiTeX has a significant influence on the graphene Dirac states, resulting in
the topologically nontrivial band structure, which is confirmed by calculated
nontrivial Z2 index and an explicit demonstration of metallic edge states. Such
heterostructures offer an unique Dirac transport system that combines the 2D
Dirac states from graphene and 1D Dirac edge states from the topological
insulator, and it offers new ideas for innovative device designs
Possible Interpretations of If It Really Exists
We analyze various possible interpretations of the narrow state
observed by SELEX Collaboration recently, which lies above
threshold and has abnormal decay pattern. These interpretations include: (1)
several versions of tetraquarks; (2) conventional meson such as the
first radial excitation of with abnormally large SU(3) symmetry
breaking; (3) conventional meson with abnormally large
coupling; (4) heavy hybrid meson. We discuss the physical implications of each
interpretation. For example, if the existence of is confirmed
as the first radial excitation of by other experiments, it will be
helpful to look for (1) its SU(3) flavor partners ; (2) its
B-meson analogues ; (3) S-wave two pion
decay modes
Fermionic partner of Quintessence field as candidate for dark matter
Quintessence is a possible candidate for dark energy. In this paper we study
the phenomenologies of the fermionic partner of Quintessence, the Quintessino.
Our results show that, for suitable choices of the model parameters, the
Quintessino is a good candidate for cold or warm dark matter. In our scenario,
dark energy and dark matter of the Universe are connected in one chiral
superfield.Comment: 4 pages, 3 figures, version to appear in PR
Ground State and Excitations of Spin Chain with Orbital Degeneracy
The one dimensional Heisenberg model in the presence of orbital degeneracy is
studied at the SU(4) symmetric viewpoint by means of Bethe ansatz. Following
Sutherland's previous work on an equivalent model, we discuss the ground state
and the low-lying excitations more extensively in connection to the spin
systems with orbital degeneracy. We show explicitly that the ground state is a
SU(4) singlet. We study the degeneracies of the elementary excitations and the
spectra of the generalized magnons consisting of these excitations. We also
discuss the complex 2-strings in the context of the Bethe ansatz solutions.Comment: Revtex, 9 pages, 3 figures; typos correcte
Isostructural Phase Transition of TiN Under High Pressure
In situ high-pressure energy dispersive x-ray diffraction experiments on
polycrystalline powder TiN with NaCl-type structure have been conducted with
the pressure up to 30.1 GPa by using the diamond anvil cell instrument with
synchrotron radiation at room tempearture. The experimental results suggested
that an isostructural phase transition might exist at about 7 GPa as revealed
by the discontinuity of V/V0 with pressure.Comment: submitte
A gauge-mediated supersymmetry breaking model with an extra singlet Higgs field
We study in some detail the next-to-minimal supersymmetric standard model
with gauge mediation of supersymmetry breaking. We find that it is feasible to
spontaneously generate values of the Higgs mass parameters and
consistent with radiative electroweak symmetry breaking. The model has a
phenomenologically viable particle spectrum. Messenger sneutrinos with mass in
the range 6 to 25 TeV can serve as cold dark matter. It is also possible to
evade the cosmological domain wall problem in this scenario.Comment: revised version to appear in PR
Infrared nanoscopy of Dirac plasmons at the graphene-SiO2 interface
We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac
fermions in graphene. This is achieved by confining mid-IR radiation at the
apex of a nanoscale tip: an approach yielding two orders of magnitude increase
in the value of in-plane component of incident wavevector q compared to free
space propagation. At these high wavevectors, the Dirac plasmon is found to
dramatically enhance the near-field interaction with mid-IR surface phonons of
SiO2 substrate. Our data augmented by detailed modeling establish graphene as a
new medium supporting plasmonic effects that can be controlled by gate voltage.Comment: 12 pages, 4 figure
Viral Decay Kinetics in the Highly Active Antiretroviral Therapy-Treated Rhesus Macaque Model of AIDS
To prevent progression to AIDS, persons infected with human immunodeficiency virus type 1 (HIV-1) must remain on highly active antiretroviral therapy (HAART) indefinitely since this modality does not eradicate the virus. The mechanisms involved in viral persistence during HAART are poorly understood, but an animal model of HAART could help elucidate these mechanisms and enable studies of HIV-1 eradication strategies. Due to the specificity of non-nucleoside reverse transcriptase (RT) inhibitors (NNRTIs) for HIV-1, we have used RT-SHIV, a chimeric virus of simian immunodeficiency virus with RT from HIV-1. This virus is susceptible to NNRTIs and causes an AIDS-like disease in rhesus macaques. In this study, two groups of HAART-treated, RT-SHIV-infected macaques were analyzed to determine viral decay kinetics. In the first group, viral loads were monitored with a standard TaqMan RT-PCR assay with a limit of detection of 50 viral RNA copies per mL. Upon initiation of HAART, viremia decayed in a bi-phasic manner with half-lives of 1.7 and 8.5 days, respectively. A third phase was observed with little further decay. In the second group, the macaques were followed longitudinally with a more sensitive assay utilizing ultracentrifugation to concentrate virus from plasma. Bi-phasic decay of viral RNA was also observed in these animals with half-lives of 1.8 and 5.8 days. Viral loads in these animals during a third phase ranged from 2–58 RNA copies/mL, with little decay over time. The viral decay kinetics observed in these macaques are similar to those reported for HIV-1 infected humans. These results demonstrate that low-level viremia persists in RT-SHIV-infected macaques despite a HAART regimen commonly used in humans
First principle study on electronic structure of ferroelectric PbFe0.5Nb0.5O3
The full potential linearized augmented plane wave (FLAPW) method was used to
study the crystal structure and electronic structure properties of
PbFe0.5Nb0.5O3 (PFN). The optimized crystal structure, density of states, band
structure and electron density distribution have been obtained to understand
the ferroelectric behavior of PFN. From the density of states analysis, it is
shown that there is a hybridization of Fe d - O p and Nb d - O p in
ferroelectric PFN. This is consistent with the calculation of electronic band
structure. This hybridization is responsible for the tendency to its
ferroelectricity.Comment: 10 page
Dark matter scenarios in the minimal SUSY B-L model
We perform a study of the dark matter candidates of a constrained version of
the minimal R-parity-conserving supersymmetric model with a gauged
. It turns out that there are four additional candidates for dark
matter in comparison to the MSSM: two kinds of neutralino, which either
correspond to the gaugino of the or to a fermionic bilepton, as
well as "right-handed" CP-even and -odd sneutrinos. The correct dark matter
relic density of the neutralinos can be obtained due to different mechanisms
including new co-annihilation regions and resonances. The large additional
Yukawa couplings required to break the radiatively often lead to
large annihilation cross sections for the sneutrinos. The correct treatment of
gauge kinetic mixing is crucial to the success of some scenarios. All
candidates are consistent with the exclusion limits of Xenon100.Comment: 45 pages, 22 figures; v2: extended discussion of direct detection
cross section, matches published versio
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