10,260 research outputs found
Magnetism and Superconductivity in a Two-band Hubbard Model in Infinite Dimensions
We study a two-band Hubbard model using the dynamical mean-field theory
combined with the exact diagonalization method. At the electron density ,
a transition from a band-insulator to a correlated semimetal occurs when the
on-site Coulomb interaction is varied for a fixed value of the
charge-transfer energy . At low temperature, the correlated semimetal
shows ferromagnetism or superconductivity. With increasing doping , the
ferromagnetic transition temperature rapidly decreases and finally becomes zero
at a critical value of . The second-order phase transition occurs at high
temperature, while a phase separation of ferromagnetic and paramagnetic states
takes place at low temperature. The superconducting transition temperature
gradually decreases and finally becomes zero near () where the
system is Mott insulator which shows antiferromagnetism at low temperature.Comment: 3 pages, 5 figures, proceedings of the International Conference on
Strongly Correlated Electrons with Orbital Degrees of Freedom (ORBITAL2001
Charge Gap in the One-Dimensional Extended Hubbard Model at Quarter Filling
We propose a new combined approach of the exact diagonalization, the
renormalization group and the Bethe ansatz for precise estimates of the charge
gap in the one-dimensional extended Hubbard model with the onsite and
the nearest-neighbor interactions and at quarter filling. This approach
enables us to obtain the absolute value of including the prefactor
without ambiguity even in the critical regime of the metal-insulator transition
(MIT) where is exponentially small, beyond usual renormalization group
methods and/or finite size scaling approaches. The detailed results of
down to of order of near the MIT are shown as contour lines on the
- plane.Comment: 4 pages, 4 figure
Random matrix model at nonzero chemical potentials with anomaly effects
Phase diagram of the chiral random matrix model with U(1)A breaking term is
studied with the quark chemical potentials varied independently at zero
temperature, by taking the chiral and meson condensates as the order
parameters. Although, without the U(1)A breaking term, chiral transition of
each flavor can happen separately responding to its chemical potential, the
U(1)A breaking terms mix the chiral condensates and correlate the phase
transitions. In the three flavor case, we find that there are mixings between
the meson and chiral condensates due to the U(1)A anomaly, which makes the
meson condensed phase more stable. Increasing the hypercharge chemical
potential () with the isospin and quark chemical potentials (,
) kept small, we observe that the kaon condensed phase becomes the
ground state and at the larger the pion condense phase appears
unexpectedly, which is caused by the competition between the chiral restoration
and the meson condensation. The similar happens when and are
exchanged, and the kaon condensed phase becomes the ground state at larger
below the full chiral restoration.Comment: 12 pages, 8 figure
Ferromagnetism and Superconductivity in the multi-orbital Hubbard Model: Hund's Rule Coupling versus Crystal-Field Splitting
The multi-orbital Hubbard model in one dimension is studied using the
numerical diagonalization method. Due to the effect of the crystal-field
splitting , the fully polarized ferromagnetism which is observed in the
strong coupling regime becomes unstable against the partially polarized
ferromagnetism when the Hund's rule coupling is smaller than a certain
critical value of order of . In the vicinity of the partially polarized
ferromagnetism, the orbital fluctuation develops due to the competition between
the Hund's rule coupling and the crystal-field splitting. The superconducting
phase with the Luttinger liquid parameter is observed for the
singlet ground state in this region.Comment: 4 pages,5 figures,submitted to J.Phys.Soc.Jp
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