6,188 research outputs found
Mott transitions in two-orbital Hubbard systems
We investigate the Mott transitions in two-orbital Hubbard systems. Applying
the dynamical mean field theory and the self-energy functional approach, we
discuss the stability of itinerant quasi-particle states in each band. It is
shown that separate Mott transitions occur at different Coulomb interaction
strengths in general. On the other hand, if some special conditions are
satisfied for the interactions, spin and orbital fluctuations are equally
enhanced at low temperatures, resulting in a single Mott transition. The phase
diagrams are obtained at zero and finite temperatures. We also address the
effect of the hybridization between two orbitals, which induces the Kondo-like
heavy fermion states in the intermediate orbital-selective Mott phase.Comment: 21 Pages, 17 Figures, to appear in Progress of Theoretical Physics
(YKIS2004 Proceedings
Angular and Abundance Distribution of High-energy Gamma Rays and Neutrons Simulated by GEANT4 Code for Solar Flares
In the solar flare observed on June 3, 2012, high energy gamma-rays and
neutrons were observed. The event includes a remarkable feature of a high
neutron/gamma-ratio in the secondary particles. We have examined whether this
high n/-ratio can be explained by simulation. As a result of
simulations using the GEANT4 program, the high n/-ratio may be
reproduced for the case that helium and other heavy ions were dominantly
accelerated in the flare.Comment: submitted to the Proceeding of The 20th International Symposium on
Very High Energy Cosmic Ray Interaction (ISVHECRI 2018, Nagoya, Japan),
Europian Physics Journa
Zero-temperature Phase Diagram of Two Dimensional Hubbard Model
We investigate the two-dimensional Hubbard model on the triangular lattice
with anisotropic hopping integrals at half filling. By means of a self-energy
functional approach, we discuss how stable the non-magnetic state is against
magnetically ordered states in the system. We present the zero-temperature
phase diagram, where the normal metallic state competes with magnetically
ordered states with and structures. It is shown
that a non-magnetic Mott insulating state is not realized as the ground state,
in the present framework, but as a meta-stable state near the magnetically
ordered phase with structure.Comment: 4 pages, 4 figure
Spin, charge and orbital fluctuations in a multi-orbital Mott insulator
The two-orbital degenerate Hubbard model with distinct hopping integrals is
studied by combining dynamical mean-field theory with quantum Monte Carlo
simulations. The role of orbital fluctuations for the nature of the Mott
transition is elucidated by examining the temperature dependence of spin,
charge and orbital susceptibilities as well as the one-particle spectral
function. We also consider the effect of the hybridization between the two
orbitals, which is important particularly close to the Mott transition points.
The introduction of the hybridization induces orbital fluctuations, resulting
in the formation of a Kondo-like heavy-fermion behavior, similarly to
electron systems, but involving electrons in bands of comparable width.Comment: 8 pages, 9 figure
Mott insulating state in a quarter-filled two-orbital Hubbard chain with different bandwidths
We investigate the ground-state properties of the one-dimensional two-band
Hubbard model with different bandwidths. The density-matrix renormalization
group method is applied to calculate the averaged electron occupancies as a
function of the chemical potential . Both at quarter and half fillings,
"charge plateaux" appear in the - plot, where diverges and
the Mott insulating states are realized. To see how the orbital polarization in
the one-quarter charge plateau develops, we apply the second-order perturbation
theory from the strong-coupling limit at quarter filling. The resultant
Kugel-Khomskii spin-orbital model includes a field coupled to
orbital pseudo-spins. This field originates from the discrepancy between the
two bandwidths and leads to a finite orbital pseudo-spin magnetization.Comment: 4 pages, 2 figures, Proceedings of LT2
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