102 research outputs found
Magnetism and superconductivity in the layered hexagonal transition metal pnictides
We investigate the electronic and magnetic structures of the 122
(AMB) hexagonal transition-metal pnictides with A=(Sr, Ca), M=(Cr, Mn,
Fe, Co, Ni) and B=(As, P, Sb). It is found that the family of materials share
critical similarities with those of tetragonal structures that include the
famous iron-based high temperature superconductors. In both families, the next
nearest neighbor(NNN) effective antiferromagnetic(AFM) exchange couplings reach
the maximum value in the iron-based materials. While the NNN couplings in the
latter are known to be responsible for the C-type AFM state and to result in
the extended s-wave superconducting state upon doping, they cause the former to
be extremely frustrated magnetic systems and can lead to an time reversal
symmetry broken superconducting state upon doping. The iron-based
compounds with the hexagonal structure, thus if synthesized, can help us to
determine the origin of high temperature superconductivity.Comment: 10 pages, 8 figure
Hybrid Crystals of Cuprates and Iron-Based Superconductors
We propose two possible new compounds, BaCuOFeAs and
KCuOFeSe, which hybridize the building blocks of two high
temperature superconductors, cuprates and iron-based superconductors. These
compounds consist of square CuO layers and antifluorite-type FeX
(X=As,Se) layers separated by Ba/K. The calculations of binding energies and
phonon spectrums indicate that they are dynamically stable, which ensures that
they may be experimentally synthesized. The Fermi surfaces and electronic
structures of the two compounds inherit the characteristics of both cuprates
and iron-based superconductors. These compounds can be superconductors with
intriguing physical properties to help to determine pairing mechanisms of high
superconductivity.Comment: 7 pages, 8 figure
A Possible Family of Ni-based High Temperature Superconductors
We suggest that a family of Ni-based compounds, which contain
[NiMO](M=chalcogen) layers with an antiperovskite structure
constructed by mixed-anion Ni complexes, NiMO, can be potential high
temperature superconductors upon doping or applying pressure. The layer
structures have been formed in many other transitional metal compounds such as
LaBSeO(B=Mn, Fe,Co). For the Ni-based compounds, we predict
that the parental compounds host collinear antiferromagnetic states similar to
those in the iron-based high temperature superconductors. The electronic
physics near Fermi energy is controlled by two e d-orbitals with
completely independent in-plane kinematics. We predict that the
superconductivity in this family is characterized by strong competition between
extended s-wave and d-wave pairing symmetries.Comment: 5 pages, 4 figure
Triplet -wave pairing in quasi one dimensional ACrAs superconductors
We construct minimum effective models to investigate the pairing symmetry in
the newly discovered quasi-one-dimensional superconductor KCrAs. We
show that a minimum three-band model based on the , and
orbitals of one Cr sublattice can capture the band structures
near Fermi surfaces. In both weak and strong coupling limits, the standard
random phase approximation (RPA) and mean-field solutions consistently yield
the triplet -wave pairing as the leading pairing symmetry for physically
realistic parameters. The triplet pairing is driven by the ferromagnetic
fluctuations within the sublattice. The gap function of the pairing state
possesses line gap nodes on the plane on the Fermi surfaces.Comment: 10 pages plus two appendix, 12 figures; Published version by Phys.
Rev.
Theoretical studies of superconductivity in doped BaCoSO
We investigate superconductivity that may exist in the doped BaCoSO, a
multi-orbital Mott insulator with a strong antiferromagnetic ground state. The
superconductivity is studied in both t-J type and Hubbard type multi-orbital
models by mean field approach and random phase approximation (RPA) analysis.
Even if there is no C4 rotational symmetry, it is found that the system still
carries a d-wave like pairing symmetry state with gapless nodes and sign
changed superconducting order parameters on Fermi surfaces. The results are
largely doping insensitive. In this superconducting state, the three t2g
orbitals have very different superconducting form factors in momentum space. In
particular, the intra-orbital pairing of the dx2-y2 orbital has a s-wave like
pairing form factor. The two methods also predict very different pairing
strength on different parts of Fermi surfaces.These results suggest that BaCoSO
and related materials can be a new ground to test and establish fundamental
principles for unconventional high temperature superconductivity.Comment: 6 pages, 7 figure
Magnetism in Quasi-One-Dimensional ACrAs (A=K,Rb) superconductors
We predict that the recently discovered quasi-one dimensional
superconductors, ACrAs(A=K,Rb), possess strong frustrated magnetic
fluctuations and are nearby a novel in-out co-planar magnetic ground state. The
frustrated magnetism is very sensitive to c-axis lattice constant and can thus
be suppressed by increasing pressure. Our results qualitatively explain strong
non-Fermi liquid behaviors observed in the normal state of the superconductors
as the intertwining between the magnetism and superconductivity can create a
large quantum critical region in quasi-one dimensional systems and also suggest
that the materials share similar phase diagrams and superconducting mechanism
with other unconventional superconductors, such as cuprates and iron-based
superconductors.Comment: published versio
The effect of As-Chain layers in CaFeAs
The new discovered iron-based superconductors have chain-like As layers.
These layers generate an additional 3-dimensional hole pocket and cone-like
electron pockets. The former is attributed to the Ca and As1 orbitals
and the latter are attributed to the anisotropic Dirac cone, contributed by As1
and orbitals. We find that large gaps on these pockets open in the
collinear antiferromagnetic ground state of CaFeAs, suggesting that the
chain-like As layers are strongly coupled to FeAs layers. Moreover due to the
low symmetry crystal induced by the As layers, the bands attributed to FeAs
layers in plane are two-fold degenerate but in plane are
lifted. This degeneracy is protected by a hidden symmetry
. Ignoring the electron cones, the materials
can be well described by a six-band model, including five Fe and As1
orbitals. We suggest that these new features may help us to identify the sign
change and pairing symmetry in iron based superconductors.Comment: 7 pages, 10 figure
Three-dimensional Critical Dirac semimetal in KMgBi
We predicted that AMgBi (A=K,Rb Cs), which have the same lattice structures
as the 111 family of iron-based superconductors (Na/LiFeAs), are
symmetry-protected Dirac semimetals located near the boundary of type-I and
type-II Dirac semimetal phases. Doping Rb or Cs into KMgBi can drive the
transition between the two phases. The materials can also be turned into Weyl
semimetals and topological insulators by explicitly or spontaneously breaking
time-reversal symmetry and C lattice symmetry respectively.Comment: 5 pages, 4 figure
CaFeAs: a Staggered Intercalation of Quantum Spin Hall and High Temperature Superconductivity
We predict that CaFeAs, a newly discovered iron-based high temperature
(T) superconductor, is a staggered intercalation compound that integrates
topological quantum spin hall (QSH) and superconductivity (SC). CaFeAs has
a structure with staggered CaAs and FeAs layers. While the FeAs layers are
known to be responsible for high T superconductivity, we show that with
spin orbital coupling each CaAs layer is a topologically nontrivial
two-dimensional QSH insulator and the bulk is a 3-dimensional weak topological
insulator. In the superconducting state, the edge states in the CaAs layer are
natural 1D topological superconductors. The staggered intercalation of QSH and
SC provides us an unique opportunity to realize and explore novel physics, such
as Majorana modes and Majorana Fermions chains.Comment: 4.5 pages, 5 figures + supplemental material,published versio
Staggered FeSe Monolayer on SrTiO (110) surface
We investigate the electronic and magnetic properties of FeSe monolayer on
the anisotropic SrTiO (110) surface. With compressive strain along
direction from the substrate, the monolayer FeSe possesses a
staggered bipartite iron lattice with an height difference around 0.06\AA~
along the out-plane direction. The staggering causes stronger magnetic
frustration between the collinear and checkerboard antiferromagnetic orders,
and the strain elongates one electron and two hole pockets along the strain
direction and the remaining hole pocket along the orthogonal direction. The
strain-induced band splitting at can also result in a band inversion
to drive the system into a topologically nontrivial phase. The absence of
strong superconducting suppression on the staggered lattice suggests that the
superconducting pairings may be insensitive to the modification of interactions
and hopping parameters between two Fe sublattices.Comment: 7 Pagges, 9 figure
- β¦