833 research outputs found
Dynamical Mean-Field Study of Metamagnetism in Heavy Fermion Systems
We investigate the metamagnetism in the periodic Anderson model with the
-dependent mixing by using the dynamical mean-field theory
combined with the exact diagonalization method. It is found that both effects
of the -dependent mixing and strong correlation due to the
Coulomb interaction between electrons are significant for determining both
the magnetization and the mass enhancement factor. For the case away from the
half-filling, the results is consistent with the metamagnetic behavior observed
in CeRuSi.Comment: 3 pages, 4 figures, accepted in J. Phys. Soc. Jpn. 80 (2011) Suppl.
(Proc. ICHE2010
Dynamical mean-field theory for the anisotropic Kondo semiconductor: Temperature and magnetic field dependence
We investigate the periodic Anderson model with -dependent -
mixing reproducing the point nodes of the hybridization gap by using the
dynamical mean-field theory combined with the exact diagonalization method. At
low temperature below a coherence temperature , the imaginary part of the
self-energy is found to be proportional to and the pseudogap with two
characteristic energies and is
clearly observed for , while the pseudogap is smeared with increasing
and then disappears at high temperature T \simg T_0 due to the evolution
of the imaginary self-energy. When the Coulomb interaction between
electrons increases, , , and
together with at which the magnetic susceptibility is
maximum decrease in proportion to the renormalization factor resulting in a
heavy-fermion semiconductor with a large mass enhancement for
large . We also examine the effect of the external magnetic field and
find that the magnetization shows two metamagnetic anomalies and
corresponding to and which
are reduced due to the effect of together with . Remarkably, is
found to be largely enhanced due to especially for H_1 \siml H \siml H_2,
where the field induced heavy-fermion state is realized. The obtained results
seem to be consistent with the experimental results observed in the anisotropic
Kondo semiconductors such as CeNiSn.Comment: 11 pages, 11 figure
A High-Tc Mechanism of Iron Pnictide Superconductivity due to Cooperation of Ferro-orbital and Antiferromagnetic Fluctuations
The electronic states and superconductivity in iron pnictides are studied on
the basis of the 16 band - model which includes both the onsite Coulomb
interaction between Fe electrons and the intersite one between Fe and
pnictogen electrons. The model well accounts for experimentally observed
two fluctuations: the - interaction-enhanced antiferromagnetic (AFM)
fluctuation and the - interaction-enhanced ferro-orbital (FO) fluctuation
responsible for the elastic softening. The AFM fluctuation induces the
repulsive pairing interaction for while the FO
does the attractive one for resulting in the -wave
superconductivity where the two fluctuations cooperatively enhance the
superconducting transition temperature without any competition by
virtue of the -space segregation.Comment: 4 pages, 4 figure
Metal-insulator transition and superconductivity in the two-orbital Hubbard-Holstein model for iron-based superconductors
We investigate a two-orbital model for iron-based superconductors to
elucidate the effect of interplay between electron correlation and Jahn-Teller
electron-phonon coupling by using the dynamical mean-field theory combined with
the exact diagonalization method. When the intra- and inter-orbital Coulomb
interactions, and , increase with , both the local spin and
orbital susceptibilities, and , increase with
in the absence of the Hund's rule coupling and the
electron-phonon coupling . In the presence of and , there are
distinct two regimes: for with the phonon
frequency , is enhanced relative to and shows a
divergence at above which the system becomes Mott insulator, while for
, is enhanced relative to
and shows a divergence at above which the system becomes
bipolaronic insulator. In the former regime, the superconductivity is mediated
by antiferromagnetic fluctuations enhanced due to Fermi-surface nesting and is
found to be largely dependent on carrier doping. On the other hand, in the
latter regime, the superconductivity is mediated by ferro-orbital fluctuations
and is observed for wide doping region including heavily doped case without the
Fermi-surface nesting.Comment: 9 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1209.495
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