24,374 research outputs found
Resonant Conversion of Massless Neutrinos in Supernovae
It has been noted for a long time that, in some circumstances, {\sl massless}
neutrinos may be {\sl mixed} in the leptonic charged current. Conventional
neutrino oscillation searches in vacuum are insensitive to this mixing. We
discuss the effects of resonant massless-neutrino conversions in the dense
medium of a supernova. In particular, we show how the detected
energy spectra from SN1987a and the supernova -process nucleosynthesis may
be used to provide very stringent constraints on the mixing of {\sl massless}
neutrinos.Comment: latex file, 20 pages, including 3 postscript figure
Gutzwiller density functional calculations of the electronic structure of FeAs-based superconductors: Evidence for a three-dimensional Fermi surface
The electronic structures of FeAs-compounds strongly depend on the
Fe-As bonding, which can not be described successfully by the local density
approximation (LDA). Treating the multi-orbital fluctuations from -
by LDA+Gutzwiller method, we are now able to predict the correct Fe-As
bond-length, and find that Fe-As bonding-strength is 30% weaker, which will
explain the observed "soft phonon". The bands are narrowed by a factor of 2,
and the orbital is pushed up to cross the Fermi level, forming
3-dimensional Fermi surfaces, which suppress the anisotropy and the ()
nesting. The inter-orbital Hund's coupling rather than plays crucial
roles to obtain these results.Comment: 4 pages, 4 figures, 1 tabl
Calorimetric Evidence of Strong-Coupling Multiband Superconductivity in Fe(Te0.57Se0.43) Single Crystal
We have investigated the specific heat of optimally-doped iron chalcogenide
superconductor Fe(Te0.57Se0.43) with a high-quality single crystal sample. The
electronic specific heat Ce of this sample has been successfully separated from
the phonon contribution using the specific heat of a non-superconducting sample
(Fe0.90Cu0.10)(Te0.57Se0.43) as a reference. The normal state Sommerfeld
coefficient gamma_n of the superconducting sample is found to be ~ 26.6 mJ/mol
K^2, indicating intermediate electronic correlation. The temperature dependence
of Ce in the superconducting state can be best fitted using a double-gap model
with 2Delta_s(0)/kBTc = 3.92 and 2Delta_l(0)/kBTc = 5.84. The large gap
magnitudes derived from fitting, as well as the large specific heat jump of
Delta_Ce(Tc)/gamma_n*Tc ~ 2.11, indicate strong-coupling superconductivity.
Furthermore, the magnetic field dependence of specific heat shows strong
evidence for multiband superconductivity
Charge collective modes in an incommensurately modulated cuprate
We report the first measurement of collective charge modes of insulating
Sr14Cu24O41 using inelastic resonant x-ray scattering over the complete
Brillouin zone. Our results show that the intense excitation modes at the
charge gap edge predominantly originate from the ladder-containing planar
substructures. The observed ladder modes (E vs. Q) are found to be dispersive
for momentum transfers along the "legs" but nearly localized along the "rungs".
Dispersion and peakwidth characteristics are similar to the charge spectrum of
1D Mott insulators, and we show that our results can be understood in the
strong coupling limit (U >> t_{ladder}> t_{chain}). The observed behavior is in
marked contrast to the charge spectrum seen in most two dimensional cuprates.
Quite generally, our results also show that momentum-tunability of inelastic
scattering can be used to resolve mode contributions in multi-component
incommensurate systems.Comment: 4+ pages, 5 figure
Quantum State Transfer Characterized by Mode Entanglement
We study the quantum state transfer (QST) of a class of tight-bonding Bloch
electron systems with mirror symmetry by considering the mode entanglement.
Some rigorous results are obtained to reveal the intrinsic relationship between
the fidelity of QST and the mirror mode concurrence (MMC), which is defined to
measure the mode entanglement with a certain spatial symmetry and is just the
overlap of a proper wave function with its mirror image. A complementarity is
discovered as the maximum fidelity is accompanied by a minimum of MMC. And at
the instant, which is just half of the characteristic time required to
accomplish a perfect QST, the MMC can reach its maximum value one. A large
class of perfect QST models with a certain spectrum structure are discovered to
support our analytical results.Comment: 6 pages, 3 figures. to appear in PR
Relation between two measures of entanglement in spin-1/2 and spinless fermion quantum chain systems
The concepts of concurrence and mode concurrence are the measures of
entanglement for spin-1/2 and spinless fermion systems respectively. Based on
the Jordan-Wigner transformation, any spin-1/2 system is always associated with
a fermion system (called counterpart system). The comparison of concurrence and
mode concurrence can be made with the aid of the Marshall's sign rule for the
ground states of spin-1/2 and spinless fermion chain systems. We observe
that there exists an inequality between concurrence and mode concurrence for
the ground states of the two corresponding systems. The spin-1/2 XY chain
system and its spinless fermion counterpart as a realistic example is discussed
to demonstrate the analytical results.Comment: 7 pages, no figures, publication version, to appear in PR
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