1,121 research outputs found
Metal-insulator transition in half-filling two-orbital Hubbard model on triangular lattice
We have investigated the half-filling two-orbital Hubbard model on a
triangular lattice by means of the dynamical mean-field theory (DMFT). The
densities of states and optical conductivity clearly show the occurence of
metal-insulating transition (MIT) at U, U=18.2, 16.8, 6.12 and 5.85
for J=0, 0.01U, U/4 and U/3, respectively. The distinct continuities of double
occupation of electrons, local square moments and local susceptibility of the
charge, the spin and the orbital at J > 0 suggest that the MIT is the
first-order; however at J=0, the MIT is the second-order in the half-filling
two-orbital Hubbard model on triangular lattices. We attribute the first-order
nature of the MIT to the low symmetry of the systems with finite Hund's
coupling J.Comment: 5 figures,13 pages, published versio
Effective mass staircase and the Fermi liquid parameters for the fractional quantum Hall composite fermions
Effective mass of the composite fermion in the fractional quantum Hall
system, which is of purely interaction originated, is shown, from a numerical
study, to exhibit a curious nonmonotonic behavior with a staircase correlated
with the number (=2,4,...) of attached flux quanta. This is surprising since
the usual composite-fermion picture predicts a smooth behavior. On top of that,
significant interactions are shown to exist between composite fermions, where
the excitation spectrum is accurately reproduced in terms of Landau's Fermi
liquid picture with negative (i.e., Hund's type) orbital and spin exchange
interactions.Comment: 4 pages, 3 figures, REVTe
Transport criticality of the first-order Mott transition in a quasi-two-dimensional organic conductor, -(BEDT-TTF)Cu[N(CN)]Cl
An organic Mott insulator, -(BEDT-TTF)Cu[N(CN)]Cl, was
investigated by resistance measurements under continuously controllable He gas
pressure. The first-order Mott transition was demonstrated by observation of
clear jump in the resistance variation against pressure. Its critical endpoint
at 38 K is featured by vanishing of the resistive jump and critical divergence
in pressure derivative of resistance, , which are consistent with the prediction of the dynamical mean field
theory and have phenomenological correspondence with the liquid-gas transition.
The present results provide the experimental basis for physics of the Mott
transition criticality.Comment: 4 pages, 5 figure
Mott Transition vs Multicritical Phenomenon of Superconductivity and Antiferromagnetism -- Application to -(BEDT-TTF)X --
Interplay between the Mott transition and the multicritical phenomenon of
d-wave superconductivity (SC) and antiferromagnetism (AF) is studied
theoretically. We describe the Mott transition, which is analogous to a
liquid-gas phase transition, in terms of an Ising-type order parameter .
We reveal possible mean-field phase diagrams produced by this interplay.
Renormalization group analysis up to one-loop order gives flows of coupling
constants, which in most cases lead to fluctuation-induced first-order phase
transitions even when the SO(5) symmetry exists betwen the SC and AF. Behaviors
of various physical quantities around the Mott critical point are predicted.
Experiments in -(BEDT-TTF)X are discussed from this viewpoint.Comment: 4 pages, 9 figures, to appear in J. Phys. Soc. Jp
Spin Chirality Fluctuation and Anomalous Hall Effect in Itinerant Ferromagnets
The anomalous Hall effect due to the spin chirality order and fluctuation is
studied theoretically in a Kondo lattice model without the relativistic
spin-orbit interaction. Even without the correlations of the localized spins,
can emerge depending on the lattice structure and the spin
anisotropy. We reveal the condition for this chirality-fluctuation driven
mechanism for . Our semiquantitative estimates for a pyrochlore
oxide NdMoO give a finite \sigma_{xy} \sim 10 \Ohm^{-1} \cm^{-1}
together with a high resistivity \rho_{xx} \sim 10^{-4}-10^{-3} \Ohm \cm, in
agreement with experiments.Comment: 5 pages, including 4 figure
Excitation spectrum and effective mass of the even-fraction quantum Hall liquid
To probe the nature of the even-fraction quantum Hall system, we have
investigated the low-lying excitation spectrum by means of exact
diagonalization for finite systems. We have found (i) a striking one-to-one
correspondence (i.e., a shell structure) between the spectrum and those for
free (composite) fermions, (ii) a surprisingly straight scaling plot for the
excitation energy that gives a zero gap (metal) in the thermodynamic limit,
(iii) the effective mass evaluated from the scaling becoming heavier for
filling factor = 1/2, 1/4, 1/6, but (iv) some deviations from the single-mode
or the Hartree-Fock composite fermion approximation as well.Comment: 4 pages, REVTeX format, 4 eps-figure
Exchange interactions and magnetic properties of the layered vanadates CaV2O5, MgV2O5, CaV3O7 and CaV4O9
We have performed ab-initio calculations of exchange couplings in the layered
vanadates CaV2O5, MgV2O5, CaV3O7 and CaV4O9. The uniform susceptibility of the
Heisenberg model with these exchange couplings is then calculated by quantum
Monte Carlo method; it agrees well with the experimental measurements. Based on
our results we naturally explain the unusual magnetic properties of these
materials, especially the huge difference in spin gap between CaV2O5 and
MgV2O5, the unusual long range order in CaV3O7 and the "plaquette resonating
valence bond (RVB)" spin gap in CaV4O9
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