5,354 research outputs found
Quasiparticle states around a nonmagnetic impurity in electron-doped iron-based superconductors with spin-density-wave order
The quasiparticle states around a nonmagnetic impurity in electron-doped
iron-based superconductors with spin-density-wave (SDW) order are investigated
as a function of doping and impurity scattering strength. In the undoped
sample, where a pure SDW state exists, two impurity-induced resonance peaks are
observed around the impurity site and they are shifted to higher (lower)
energies as the strength of the positive (negative) scattering potential (SP)
is increased. For the doped samples where the SDW order and the superconducting
order coexist, the main feature is the existence of sharp in-gap resonance
peaks whose positions and intensity depend on the strength of the SP and the
doping concentration. In all cases, the local density of states exhibits clear
symmetry. We also note that in the doped cases, the impurity will divide
the system into two sublattices with distinct values of magnetic order. Here we
use the band structure of a two-orbital model, which considers the asymmetry of
the As atoms above and below the Fe-Fe plane. This model is suitable to study
the properties of the surface layers in the iron-pnictides and should be more
appropriate to describe the scanning tunneling microscopy experiments.Comment: 11 pages, 18 figure
Study on the immobilisation mechanism of chromium under microwave sintering
Chromium (Cr) salts have been widely used in various industries and the discharged waste has caused soil
contamination. Among them, Cr(VI) is the main concern due to its high solubility and strong carcinogenic
properties. This paper compares the performance of a novel microwave sintering technique with the
conventional sintering technique for immobilising Cr contaminated soil. The most significant advantage of the
microwave sintering is that it can provide controlled atmosphere (such as reduction atmosphere), which
means Cr(Vl) can be reduced to less hazardous Cr(III) during the sintering process. The potential secondary
contamination can, thus, be significantly reduced. The XRD results show that with microwave sintering,
stronger and sharper peaks were observed, indicating minerals with higher crystallinity have been formed.
On the other hand, the SEM results reveal that with conventional electric sintering, the microstructure was
dominated by glassy phases, whilst a mixture of glassy and crystalline phases has been identified with
microwave sintering. The leaching results show that the contaminated soil processed with microwave has
met both British and Chinese leaching standards, and is better than that from the electric sintering technique
Lasing oscillation condition and group delay control in gain-assisted plasmon-induced transparency
A gain-assisted plasmonic waveguide with two detuned resonators is
investigated in the plasmon-induced transparency window. Phase map is employed
to study power transmittance and group delay for varying gain coefficients and
frequency detunings of the two resonators. The gain coefficient for lasing
oscillation condition is analytically shown to vary quadratically with the
frequency detuning. In the amplification regime below the lasing threshold, the
spectrum implies not only large group delay, but also high transmittance and
narrow linewidth. This is in contrast to those in the loss-compensation regime
and the passive case in which there always exists a trade-off between the
linewidth and the peak transmittance.Comment: 15 pages, 4 figure
Stability of Pairwise Entanglement in a Decoherent Environment
Consider the dynamics of a two-qubit entangled system in the decoherence
environment, we investigate the stability of pairwise entanglement under
decoherence. We find that for different decoherence models, there exist some
special class of entangled states of which the pairwise entanglement is the
most stable. The lifetime of the entanglement in these states is larger than
other states with the same initial entanglement. In addition, we also
investigate the dynamics of pairwise entanglement in the ground state of spin
models such as Heisenberg and XXY models.Comment: accepted by Physical Review A, references updated and minor change
Local Operations in qubit arrays via global but periodic Manipulation
We provide a scheme for quantum computation in lattice systems via global but
periodic manipulation, in which only effective periodic magnetic fields and
global nearest neighbor interaction are required. All operations in our scheme
are attainable in optical lattice or solid state systems. We also investigate
universal quantum operations and quantum simulation in 2 dimensional lattice.
We find global manipulations are superior in simulating some nontrivial many
body Hamiltonians.Comment: 5 pages, 2 figures, to appear in Phys. Rev.
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