345 research outputs found
Band structure renormalization and weak pseudogap behavior in Na_{0.33}CoO_2: Fluctuation exchange study based on a single band model
Based on a single band Hubbard model and the fluctuation exchange
approximation, the effective mass and the energy band renormalization in
NaCoO is elaborated. The renormalization is observed to exhibit
certain kind of anisotropy, which agrees qualitatively with the angle-resolved
photoemission spectroscopy (ARPES) measurements. Moreover, the spectral
function and density of states (DOS) in the normal state are calculated, with a
weak pseudogap behavior being seen, which is explained as a result of the
strong Coulomb correlations. Our results suggest that the large Fermi surface
(FS) associated with the band plays likely a central role in the
charge dynamics.Comment: 5 pages, 5 figure
Orbital-transverse density-wave instabilities in iron-based superconductors
Besides the conventional spin-density-wave (SDW) state, a new kind of
orbital-transverse density-wave (OTDW) state is shown to exist generally in
multi-orbital systems. We demonstrate that the orbital character of Fermi
surface nesting plays an important role in density responses. The relationship
between antiferromagnetism and structural phase transition in LaFeAsO (1111)
and BaFeAs (122) compounds of iron-based superconductors may be
understood in terms of the interplay between the SDW and OTDW with a
five-orbital Hamiltonian. We propose that the essential difference between 1111
and 122 compounds is crucially determined by the presence of the
two-dimensional -like Fermi surface around (0,0) being only in 1111
parent compounds.Comment: several parts were rewritten for clarity. 6 pages, 3 figures, 1 tabl
Possible singlet and triplet superconductivity on honeycomb lattice
We study the possible superconducting pairing symmetry mediated by spin and
charge fluctuations on the honeycomb lattice using the extended Hubbard model
and the random-phase-approximation method. From to doping levels,
a spin-singlet -wave is shown to be the leading
superconducting pairing symmetry when only the on-site Coulomb interaction
is considered, with the gap function being a mixture of the nearest-neighbor
and next-nearest-neighbor pairings. When the offset of the energy level between
the two sublattices exceeds a critical value, the most favorable pairing is a
spin-triplet -wave which is mainly composed of the next-nearest-neighbor
pairing. We show that the next-nearest-neighbor Coulomb interaction is also
in favor of the spin-triplet -wave pairing.Comment: 6 pages, 4 figure
Superconducting proximity effect to the block antiferromagnetism in KFeSe
Recent discovery of superconducting (SC) ternary iron selenides has block
antiferromagentic (AFM) long range order. Many experiments show possible
mesoscopic phase separation of the superconductivity and antiferromagnetism,
while the neutron experiment reveals a sizable suppression of magnetic moment
due to the superconductivity indicating a possible phase coexistence. Here we
propose that the observed suppression of the magnetic moment may be explained
due to the proximity effect within a phase separation scenario. We use a
two-orbital model to study the proximity effect on a layer of block AFM state
induced by neighboring SC layers via an interlayer tunneling mechanism. We
argue that the proximity effect in ternary Fe-selenides should be large because
of the large interlayer coupling and weak electron correlation. The result of
our mean field theory is compared with the neutron experiments
semi-quantitatively. The suppression of the magnetic moment due to the SC
proximity effect is found to be more pronounced in the d-wave superconductivity
and may be enhanced by the frustrated structure of the block AFM state.Comment: 6 pages, 6 figure
Theory for charge and orbital density-wave states in manganite LaSrMnO
We investigate the high temperature phase of layered manganites, and
demonstrate that the charge-orbital phase transition without magnetic order in
LaSrMnO can be understood in terms of the density wave
instability. The orbital ordering is found to be induced by the nesting between
segments of Fermi surface with different orbital characters. The simultaneous
charge and orbital orderings are elaborated with a mean field theory. The
ordered orbitals are shown to be .Comment: published versio
Single nonmagnetic impurity resonance in FeSe-based 122-type superconductors as a probe for pairing symmetry
We study the effect of a single non-magnetic impurity in
AFeSe (A=K, Rb, or Cs) superconductors by considering
various pairing states based on a three-orbital model consistent with the
photoemission experiments. The local density of states on and near the impurity
site has been calculated by solving the Bogoliubov-de Gennes equations
self-consistently. The impurity-induced in-gap bound states are found only for
attractive impurity scattering potential, as in the cases of doping of Co or
Ni, which is characterized by the strong particle-hole asymmetry, in the
nodeless wave pairing state. This property may be used to probe
the pairing symmetry of FeSe-based 122-type superconductors.Comment: 7 pages, 7 figure
- …