764 research outputs found
Competition between singlet and triplet pairings in Na_xCoO_2 yH_2O
We discuss the pairing symmetry of a cobaltate superconductor
NaCoO HO by adopting an effective single band model that
takes into account the hole pockets, as discussed in our previous paper
[to appear in Phys. Rev. Lett.] Here we consider the off-site repulsions in
addition to the on-site repulsion considered in our previous study. We show
that the spin-triplet f-wave pairing proposed in our previous study is robust
to some extent even in the presence of off-site repulsions. However, f-wave
pairing gives way to singlet pairings for sufficiently large values of off-site
repulsions. Among the singlet pairings, i-wave and extended s-wave pairings are
good candidates which do not break time reversal symmetry below in
agreement with the experiments.Comment: 12 page
Spin-triplet superconductivity in repulsive Hubbard models with disconnected Fermi surfaces: a case study on triangular and honeycomb lattices
We propose that spin-fluctuation-mediated spin-triplet superconductivity may
be realized in repulsive Hubbard models with disconnected Fermi surfaces. The
idea is confirmed for Hubbard models on triangular (dilute band filling) and
honeycomb (near half-filling) lattices using fluctuation exchange
approximation, where triplet pairing order parameter with f-wave symmetry is
obtained. Possible relevance to real superconductors is suggested.Comment: 5 pages, 6 figures, RevTeX, uses epsf.sty and multicol.st
Giant magneto-optical response in non-magnetic semiconductor BiTeI driven by bulk Rashba spin splitting
We study the magneto-optical (MO) response of polar semiconductor BiTeI with
giant bulk Rashba spin splitting at various carrier densities. Despite being
non-magnetic, the material is found to yield a huge MO activity in the infrared
region under moderate magnetic fields (<3 T). By comparison with
first-principles calculations, we show that such an enhanced MO response is
mainly due to the intraband transitions between the Rashba-split bulk
conduction bands in BiTeI, which give rise to distinct novel features and
systematic doping dependence of the MO spectra. We further predict an even more
pronounced enhancement in the low-energy MO response and dc Hall effect near
the crossing (Dirac) point of the conduction bands
First-principles study on the origin of large thermopower in hole-doped LaRhO3 and CuRhO2
Based on first-principles calculations, we study the origin of the large
thermopower in Ni-doped LaRhO3 and Mg-doped CuRhO2. We calculate the band
structure and construct the maximally localized Wannier functions from which a
tight binding Hamiltonian is obtained. The Seebeck coefficient is calculated
within the Boltzmann's equation approach using this effective Hamiltonian. For
LaRhO3, we find that the Seebeck coefficient remains nearly constant within a
large hole concentration range, which is consistent with the experimental
observation. For CuRhO2, the overall temperature dependence of the calculated
Seebeck coefficient is in excellent agreement with the experiment. The origin
of the large thermopower is discussed.Comment: 7 pages, to be published J. Phys.: Cond. Matt., Proc. QSD 200
High-pressure synthesis of Ba2RhO4, a rhodate analog of the layered perovskite Sr-ruthenate
A layered perovskite-type oxide Ba2RhO4 was synthesized by a high-pressure technique with the support of convex-hull calculations. The crystal and electronic structure were studied by both experimental and computational tools. Structural refinements for powder x-ray diffraction data showed that Ba2RhO4 crystallizes in a K2NiF4-type structure, isostructural to Sr2RuO4 and Ba2IrO4. Magnetic, resistivity, and specific-heat measurements for polycrystalline samples of Ba2RhO4 indicate that the system can be characterized as a correlated metal. Despite the close similarity to its Sr2RuO4 counterpart in the electronic specific-heat coefficient and the Wilson ratio, Ba2RhO4 shows no signature of superconductivity down to 0.16 K. Whereas the Fermi surface topology has reminiscent pieces of Sr2RuO4, an electronlike eg-(dx2-y2) band descends below the Fermi level, making this compound unique also as a metallic counterpart of the spin-orbit coupled Mott insulator Ba2IrO4
Ferromagnetic Luttinger Liquids
We study weak itinerant ferromagnetism in one-dimensional Fermi systems using
perturbation theory and bosonization. We find that longitudinal spin
fluctuations propagate ballistically with velocity v_m << v_F, where v_F is the
Fermi velocity. This leads to a large anomalous dimension in the spin-channel
and strong algebraic singularities in the single-particle spectral function and
in the transverse structure factor for momentum transfers q ~ 2 Delta/v_F,
where 2 Delta is the exchange splitting.Comment: 4 pages, 3 figure
High-energy scale revival and giant kink in the dispersion of a cuprate superconductor
In the present photoemission study of a cuprate superconductor
Bi1.74Pb0.38Sr1.88CuO6+delta, we discovered a large scale dispersion of the
lowest band, which unexpectedly follows the band structure calculation very
well. The incoherent nature of the spectra suggests that the hopping-dominated
dispersion occurs possibly with the assistance of local spin correlations. A
giant kink in the dispersion is observed, and the complete self-energy
containing all interaction information is extracted for a doped cuprate in the
low energy region. These results recovered significant missing pieces in our
current understanding of the electronic structure of cuprates.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett. on May 21, 200
Bulk and surface-sensitive high-resolution photoemission study of Mott-Hubbard systems SrVO and CaVO
We study the electronic structure of Mott-Hubbard systems SrVO and
CaVO with bulk and surface-sensitive high-resolution photoemission
spectroscopy (PES), using a VUV laser, synchrotron radiation and a discharge
lamp ( = 7 - 21 eV). A systematic suppression of the density of states
(DOS) within 0.2 eV of the Fermi level () is found on decreasing
photon energy i.e. on increasing bulk sensitivity. The coherent band in
SrVO and CaVO is shown to consist of surface and bulk derived
features, separated in energy. The stronger distortion on surface of CaVO
compared to SrVO leads to higher surface metallicity in the coherent DOS
at , consistent with recent theory.Comment: 4 pages 5 figures (including 2 auxiliary figures); A complete
analysis of the spectra based on the surface and bulk analysis shows in
auxiliary figures Fig. A1 and A
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