22,278 research outputs found
Electronic structures of antiperovskite superconductors: MgXNi (X=B,C,N)
We have investigated electronic structures of a newly discovered
antiperovskite superconductor MgCNi and related compounds MgBNi and
MgNNi. In MgCNi, a peak of very narrow and high density of states is
located just below , which corresponds to the antibonding
state of Ni-3d and C- but with the predominant Ni-3d character. The
prominent nesting feature is observed in the -centered electron Fermi
surface of an octahedron-cage-like shape that originates from the 19th band.
The estimated superconducting parameters based on the simple rigid-ion
approximation are in reasonable agreement with experiment, suggesting that the
superconductivity in MgCNi is described well by the conventional phonon
mechanism.Comment: 5 pages, 5 figure
Electronic Structures of Antiperovskite Superconductor MgCNi and Related Compounds
Electronic structure of a newly discovered antiperovskite superconductor
MgCNi is investigated by using the LMTO band method. The main contribution
to the density of states (DOS) at the Fermi energy comes from Ni
3 states which are hybridized with C 2 states. The DOS at is
varied substantially by the hole or electron doping due to the very high and
narrow DOS peak located just below . We have also explored
electronic structures of C-site and Mg-site doped MgCNi systems, and
described the superconductivity in terms of the conventional phonon mechanism.Comment: 3 pages, presented at ORBITAL2001 September 11-14, 2001 (Sendai,
JAPAN
Electronic structure of metallic antiperovskite compound GaCMn
We have investigated electronic structures of antiperovskite GaCMn and
related Mn compounds SnCMn, ZnCMn, and ZnNMn. In the paramagnetic
state of GaCMn, the Fermi surface nesting feature along the
direction is observed, which induces the antiferromagnetic (AFM) spin ordering
with the nesting vector {\bf Q} . Calculated
susceptibilities confirm the nesting scenario for GaCMn and also explain
various magnetic structures of other antiperovskite compounds. Through the band
folding effect, the AFM phase of GaCMn is stabilized. Nearly equal
densities of states at the Fermi level in the ferromagnetic and AFM phases of
GaCMn indicate that two phases are competing in the ground state.Comment: 4 pages, 5 figure
Large anisotropy in the optical conductivity of YNi2B2C
The optical properties of YNiBC are studied by using the
first-principles full-potential linearized augmented plane wave (FLAPW) method
within the local density approximation. Anisotropic behavior is obtained in the
optical conductivity, even though the electronic structure shows 3D character.
A large peak in is obtained at 2.4 eV. The anisotropic optical
properties are analyzed in terms of interband transitions between energy levels
and found that the Ni site plays an important role. The electronic energy loss
spectroscopy (EELS) spectra are also calculated to help elucidate the
anisotropic properties in this system.Comment: revtex4, 4 pages, 5 figures, to appear in PR
Superspace Formulation in a Three-Algebra Approach to D=3, N=4,5 Superconformal Chern-Simons Matter Theories
We present a superspace formulation of the D=3, N=4,5 superconformal
Chern-Simons Matter theories, with matter supermultiplets valued in a
symplectic 3-algebra. We first construct an N=1 superconformal action, and then
generalize a method used by Gaitto and Witten to enhance the supersymmetry from
N=1 to N=5. By decomposing the N=5 supermultiplets and the symplectic 3-algebra
properly and proposing a new super-potential term, we construct the N=4
superconformal Chern-Simons matter theories in terms of two sets of generators
of a (quaternion) symplectic 3-algebra. The N=4 theories can also be derived by
requiring that the supersymmetry transformations are closed on-shell. The
relationship between the 3-algebras, Lie superalgebras, Lie algebras and
embedding tensors (proposed in [E. A. Bergshoeff, O. Hohm, D. Roest, H.
Samtleben, and E. Sezgin, J. High Energy Phys. 09 (2008) 101.]) is also
clarified. The general N=4,5 superconformal Chern-Simons matter theories in
terms of ordinary Lie algebras can be rederived in our 3-algebra approach. All
known N=4,5 superconformal Chern-Simons matter theories can be recovered in the
present superspace formulation for super-Lie-algebra realization of symplectic
3-algebras.Comment: 37 pages, minor changes, published in PR
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