21,801 research outputs found
BaFe2As2 Surface Domains and Domain Walls: Mirroring the Bulk Spin Structure
High-resolution scanning tunneling microscopy (STM) measurements on
BaFe2As2-one of the parent compounds of the iron-based superconductors-reveals
a (1x1) As-terminated unit cell on the (001) surface. However, there are
significant differences of the surface unit cell compared to the bulk: only one
of the two As atoms in the unit cell is imaged and domain walls between
different (1x1) regions display a C2 symmetry at the surface. It should have
been C2v if the STM image reflected the geometric structure of the surface or
the orthorhombic bulk. The inequivalent As atoms and the bias dependence of the
domain walls indicate that the origin of the STM image is primarily electronic
not geometric. We argue that the surface electronic topography mirrors the bulk
spin structure of BaFe2As2, via strong orbital-spin coupling
A Note on Gauss-Bonnet Holographic Superconductors
We present an analytic treatment near the phase transition for the critical
temperature of (3+1)-dimensional holographic superconductors in
Einstein-Gauss-Bonnet gravity with backreaction. We find that the backreaction
makes the critical temperature of the superconductor decrease and condensation
harder. This is consistent with previous numerical results.Comment: 6 pages, typos corrected, references added, published versio
Comment on "Quantum key distribution without alternative measurements"
In a recent paper [A. Cabello, Phys. Rev. A 61, 052312 (2000)], a quantum key
distribution protocol based on entanglement swapping was proposed. However, in
this comment, it is shown that this protocol is insecure if Eve use a special
strategy to attack.Comment: 2 Pages, 1 Figur
Quasispecies distribution of Eigen model
We study sharp peak landscapes (SPL) of Eigen model from a new perspective
about how the quasispecies distribute in the sequence space. To analyze the
distribution more carefully, we bring forth two tools. One tool is the variance
of Hamming distance of the sequences at a given generation. It not only offers
us a different avenue for accurately locating the error threshold and
illustrates how the configuration of the distribution varies with copying
fidelity in the sequence space, but also divides the copying fidelity into
three distinct regimes. The other tool is the similarity network of a certain
Hamming distance , by which we can get a visual and in-depth result
about how the sequences distribute. We find that there are several local optima
around the center (global optimum) in the distribution of the sequences
reproduced near the threshold. Furthermore, it is interesting that the
distribution of clustering coefficient follows lognormal distribution
and the curve of clustering coefficient of the network versus
appears as linear behavior near the threshold.Comment: 13 pages, 6 figure
Universal quasiparticle decoherence in hole- and electron-doped high-Tc cuprates
We use angle-resolved photoemission to unravel the quasiparticle decoherence
process in the high- cuprates. The coherent band is highly renormalized,
and the incoherent part manifests itself as a nearly vertical ``dive'' in the
- intensity plot that approaches the bare band bottom. We find that the
coherence-incoherence crossover energies in the hole- and electron-doped
cuprates are quite different, but scale to their corresponding bare bandwidth.
This rules out antiferromagnetic fluctuations as the main source for
decoherence. We also observe the coherent band bottom at the zone center, whose
intensity is strongly suppressed by the decoherence process. Consequently, the
coherent band dispersion for both hole- and electron-doped cuprates is
obtained, and is qualitatively consistent with the framework of Gutzwiller
projection.Comment: 4 pages, 4 figure
Critical Current Density and Resistivity of MgB2 Films
The high resistivity of many bulk and film samples of MgB2 is most readily
explained by the suggestion that only a fraction of the cross-sectional area of
the samples is effectively carrying current. Hence the supercurrent (Jc) in
such samples will be limited by the same area factor, arising for example from
porosity or from insulating oxides present at the grain boundaries. We suggest
that a correlation should exist, Jc ~ 1/{Rho(300K) - Rho(50K)}, where Rho(300K)
- Rho(50K) is the change in the apparent resistivity from 300 K to 50 K. We
report measurements of Rho(T) and Jc for a number of films made by hybrid
physical-chemical vapor deposition which demonstrate this correlation, although
the "reduced effective area" argument alone is not sufficient. We suggest that
this argument can also apply to many polycrystalline bulk and wire samples of
MgB2.Comment: 11 pages, 3 figure
Elliptic flow in heavy ion collisions near the balance energy
The proton elliptic flow in collisions of Ca on Ca at energies from 30 to 100
MeV/nucleon is studied in an isospin-dependent transport model. With increasing
incident energy, the elliptic flow shows a transition from positive to negative
flow. Its magnitude depends on both the nuclear equation of state (EOS) and the
nucleon-nucleon scattering cross section. Different elliptic flows are obtained
for a stiff EOS with free nucleon-nucleon cross sections and a soft EOS with
reduced nucleon-nucleon cross sections, although both lead to vanishing
in-plane transverse flow at the same balance energy. The study of both in-plane
and elliptic flows at intermediate energies thus provides a means to extract
simultaneously the information on the nuclear equation of state and the
nucleon-nucleon scattering cross section in medium.Comment: 6 pages, 2 figure
Surface Geometric and Electronic Structure of BaFe2As2(001)
BaFe2As2 exhibits properties characteristic of the parent compounds of the
newly discovered iron (Fe)-based high-TC superconductors. By combining the real
space imaging of scanning tunneling microscopy/spectroscopy (STM/S) with
momentum space quantitative Low Energy Electron Diffraction (LEED) we have
identified the surface plane of cleaved BaFe2As2 crystals as the As terminated
Fe-As layer - the plane where superconductivity occurs. LEED and STM/S data on
the BaFe2As2(001) surface indicate an ordered arsenic (As) - terminated
metallic surface without reconstruction or lattice distortion. It is surprising
that the STM images the different Fe-As orbitals associated with the
orthorhombic structure, not the As atoms in the surface plane.Comment: 12 pages, 4 figure
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