7,985 research outputs found
Orbital-dependent effects of electron correlations in microscopic models for iron-based superconductors
The bad metal behavior in the normal state of the iron-based superconductors
suggests an intimate connection between the superconductivity and a proximity
to a Mott transition. At the same time, there is strong evidence for the
multi-orbital nature of the electronic excitations. It is then important to
understand the orbital-dependent effects of electron correlations. In this
paper we review the recent theoretical progresses on the metal-to-insulator
transition in multiorbital models for the iron-based superconductors. These
include studies of models that contain at least the 3d xy and 3d xz/yz models,
using a slave-spin technique. For commensurate filling corresponding to that of
the parent iron pnictides and chalcogenideds, a Mott transition generally
exists in all these models. Near the Mott transition, a strongly correlated
metal exhibiting bad metal features and strong orbital selectivity is
stabilized due to the interplay of Hund's coupling and orbital-degeneracy
breaking. Particularly for the alkaline iron selenides, the ordered vacancies
effectively reduce the kinetic energy, thereby pushing the system further into
the Mott-insulating regime; in the metallic state, there exists an
orbital-selective Mott phase in which the iron 3d xy orbital is Mott localized
while the other 3d orbitals are still itinerant. An overall phase diagram for
the alkaline iron selenides has been proposed, in which the orbital-selective
Mott phase connects between the superconducting phase and the Mott-insulating
parent state.Comment: 20 pages, 7 figures, to appear in a special issue of Current Opinion
in Solid State & Materials Science on "Fe-based superconductors
Orbital-selective superconductivity, gap anisotropy and spin resonance excitations in a multiorbital t-J1-J2 model for iron pnictides
We study the orbital-dependent superconducting pairing in a five-orbital
t-J1-J2 model for iron pnictides. Depending on the orbital selectivity of
electron correlations and the orbital characters along the Fermi surface, the
superconducting gap in an A_{1g} pairing state may exhibit anisotropy. This
anisotropy varies with the degree of J1-J2 magnetic frustration. We have also
calculated the dynamical spin susceptibility in the superconducting state. The
frequency dependence of the susceptibility at the antiferromagnetic wavevector
(\pi,0) shows a resonance, whose width is enhanced by the orbital dependence of
the superconducting gap; when the latter is sufficiently strong, the resonance
peak may be split into two. We discuss the implications of our results on the
recent angle-resolved photoemission and neutron-scattering measurements in
several superconducting iron pnictides.Comment: 4.5 pages, 3 figures, with supplementary material
Orbital selectivity enhanced by nematic order in FeSe
Motivated by the recent low-tempearture experiments on bulk FeSe, we study
the electron correlation effects in a multiorbital model for this compound in
the nematic phase using the U(1) slave-spin theory. We find that a finite
nematic order helps to stabilize an orbital selective Mott phase. Moreover, we
propose that when the d- and s-wave bond nematic orders are combined with the
ferro-orbital order, there exists a surprisingly large orbital selectivity
between the xz and yz orbitals even though the associated band splitting is
relatively small. Our results explain the seemingly unusual observation of
strong orbital selectivity in the nematic phase of FeSe, and uncover new clues
on the nature of the nematic order, and sets the stage to elucidate the
interplay between superconductivity and nematicity in iron-based
superconductors.Comment: 4 pages, 4 figures with 5 pages, 5 figures in supplementary material,
published versio
A hybrid model approach for strange and multi-strange hadrons in 2.76 A TeV Pb+Pb collisions
Using the VISHNU hybrid model, we calculate the multiplicity, spectra, and
elliptic flow of , and in 2.76 A TeV Pb+Pb collisions.
Comparisons between our calculations and the ALICE measurements show that the
model generally describes the soft hadron data of these strange and
multi-strange hadrons at several centrality bins. Mass ordering of elliptic
flow among , K, p, , and has also been studied and
discussed. With a nice description of the particle yields, we explore chemical
and thermal freeze-out of various hadrons species at the LHC within the
framework of the VISHNU hybrid model.Comment: version 2: with several references added, published in PR
Isobaric Reconstruction of the Baryonic Acoustic Oscillation
In this paper, we report a significant recovery of the linear baryonic
acoustic oscillation (BAO) signature by applying the isobaric reconstruction
algorithm to the non-linear matter density field. Assuming only the
longitudinal component of the displacement being cosmologically relevant, this
algorithm iteratively solves the coordinate transform between the Lagrangian
and Eulerian frames without requiring any specific knowledge of the dynamics.
For dark matter field, it produces the non-linear displacement potential with
very high fidelity. The reconstruction error at the pixel level is within a few
percent, and is caused only by the emergence of the transverse component after
the shell-crossing. As it circumvents the strongest non-linearity of the
density evolution, the reconstructed field is well-described by linear theory
and immune from the bulk-flow smearing of the BAO signature. Therefore this
algorithm could significantly improve the measurement accuracy of the sound
horizon scale. For a perfect large-scale structure survey at redshift zero
without Poisson or instrumental noise, the fractional error is reduced by a
factor of 2.7, very close to the ideal limit with linear power spectrum and
Gaussian covariance matrix.Comment: 5 pages, 3 figures, accepted versio
Entanglement R\'enyi -entropy
We study the entanglement R\'{e}nyi -entropy (ERE) as the
measure of entanglement. Instead of a single quantity in standard entanglement
quantification for a quantum state by using the von Neumann entropy for the
well-accepted entanglement of formation (EoF), the ERE gives a
continuous spectrum parametrized by variable as the entanglement
measure, and it reduces to the standard EoF in the special case . The ERE provides more information in entanglement
quantification, and can be used such as in determining the convertibility of
entangled states by local operations and classical communication. A series of
new results are obtained: (i) we can show that ERE of two states,
which can be mixed or pure, may be incomparable, in contrast to the fact that
there always exists an order for EoF of two states; (ii) similar as the case of
EoF, we study in a fully analytical way the ERE for arbitrary
two-qubit states, the Werner states and isotropic states in general
d-dimension; (iii) we provide a proof of the previous conjecture for the
analytical functional form of EoF of isotropic states in arbitrary d-dimension.Comment: 11 pages, 4 figure
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