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Search Results: 1 - 10 of 1193 matches for " Norio Ohashi "
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Mott transition in Kagomé lattice Hubbard model
Takuma Ohashi,Norio Kawakami,Hirokazu Tsunetsugu
Physics , 2006, DOI: 10.1103/PhysRevLett.97.066401
Abstract: We investigate the Mott transition in the Kagom\'e lattice Hubbard model using a cluster extension of dynamical mean field theory. The calculation of the double occupancy, the density of states, the static and dynamical spin correlation functions demonstrates that the system undergoes the first-order Mott transition at the Hubbard interaction $U/W \sim 1.4$ ($W$:bandwidth). In the metallic phase close to the Mott transition, we find the strong renormalization of three distinct bands, giving rise to the formation of heavy quasiparticles with strong frustration. It is elucidated that the quasiparticle states exhibit anomalous behavior in the temperature-dependent spin correlation functions.
Finite-Temperature Mott Transition in Two-Dimensional Frustrated Hubbard Models
Takuma Ohashi,Tsutomu Momoi,Hirokazu Tsunetsugu,Norio Kawakami
Physics , 2008, DOI: 10.1143/PTPS.176.97
Abstract: We investigate the Hubbard model on two typical frustrated lattices in two dimensions, the kagome lattice and the anisotropic triangular lattice, by means of the cellular dynamical mean field theory. We show that the metallic phase is stabilized up to fairly large Hubbard interactions under strong geometrical frustration in both cases, which results in heavy fermion behavior and several anomalous properties around the Mott transition point. In particular, for the anisotropic triangular lattice, we find novel reentrant behavior in the Mott transition in the moderately frustrated parameter regime, which is caused by the competition between Fermi-liquid formation and magnetic correlations. It is demonstrated that the reentrant behavior is a generic feature inherent in the Mott transition with intermediate geometrical frustration, and indeed in accordance with recent experimental findings for organic materials.
Periodic Anderson model with degenerate orbitals: linearized dynamical mean field theory approach
Ryota Sato,Takuma Ohashi,Akihisa Koga,Norio Kawakami
Physics , 2004, DOI: 10.1143/JPSJ.73.1864
Abstract: We investigate a multi-orbital extension of the periodic Anderson model with particular emphasis on electron correlations including orbital fluctuations. By means of a linearized version of the dynamical mean-field theory, we compute the renormalization factor, the density of states, the spectral gap and the local correlation functions for a given set of the intra- and inter-orbital Coulomb interactions as well as the Hund coupling. It is found that when a certain condition is met for the intra- and inter-orbital interactions for $f$ electrons, orbital fluctuations are enhanced, thereby enlarging the Kondo insulating gap. This effect is suppressed in the presence of the Hund coupling. We also clarify how the Kondo insulator is continuously changed to the Mott insulator when electron correlations among conduction electrons are increased.
Mott transition in the Hubbard model on the anisotropic kagomé lattice
Yuta Furukawa,Takuma Ohashi,Yohta Koyama,Norio Kawakami
Physics , 2010, DOI: 10.1103/PhysRevB.82.161101
Abstract: We investigate the Mott transition in the anisotropic kagom\'e lattice Hubbard model using the cellular dynamical mean field theory combined with continuous-time quantum Monte Carlo simulations. By calculating the double occupancy and the density of states, we determine the interaction strength of the first-order Mott transition and show that it becomes small as the anisotropy increases. We also calculate the spin correlation functions and the single-particle spectrum, and reveal that the quasiparticle and magnetic properties change dramatically around the Mott transition; the spin correlations are strongly enhanced and the quasiparticle bands are deformed. We conclude that such dramatic changes are due to the enhancement of anisotropy associated with the relaxation of frustration around the Mott transition.
Finite temperature Mott transition in Hubbard model on anisotropic triangular lattice
Takuma Ohashi,Tsutomu Momoi,Hirokazu Tsunetsugu,Norio Kawakami
Physics , 2007, DOI: 10.1103/PhysRevLett.100.076402
Abstract: We investigate the Hubbard model on the anisotropic triangular lattice by means of the cellular dynamical mean field theory. The phase diagram determined in the Hubbard interaction versus temperature plane shows novel reentrant behavior in the Mott transition due to the competition between Fermi-liquid formation and magnetic correlations under geometrical frustration. We demonstrate that the reentrant behavior is characteristic of the Mott transition with intermediate geometrical frustration and indeed consistent with recent experimental results of organic materials.
Field-induced phase transition in the periodic Anderson model
Takuma Ohashi,Akihisa Koga,Sei-ichiro Suga,Norio Kawakami
Physics , 2004, DOI: 10.1016/j.physb.2005.01.211
Abstract: We investigate the effect of magnetic fields on a Kondo insulator by using the periodic Anderson model. The analysis by dynamical mean field theory combined with quantum Monte Carlo simulations reveals that the magnetic field drives the Kondo insulator to a transverse antiferromagnetic insulator at low temperatures. We calculate the staggered spin susceptibility and find its divergence signaling the antiferromagnetic instability. Further investigation of the spin correlation functions and the magnetization process clarifies how the magnetic field suppresses the Kondo singlet formation and induces the transverse antiferromagnetic ordering.
Field-induced phase transitions in a Kondo insulator
Takuma Ohashi,Akihisa Koga,Sei-ichiro Suga,Norio Kawakami
Physics , 2004, DOI: 10.1103/PhysRevB.70.245104
Abstract: We study the magnetic-field effect on a Kondo insulator by exploiting the periodic Anderson model with the Zeeman term. The analysis using dynamical mean field theory combined with quantum Monte Carlo simulations determines the detailed phase diagram at finite temperatures. At low temperatures, the magnetic field drives the Kondo insulator to a transverse antiferromagnetic phase, which further enters a polarized metallic phase at higher fields. The antiferromagnetic transition temperature $T_c$ takes a maximum when the Zeeman energy is nearly equal to the quasi-particle gap. In the paramagnetic phase above $T_c$, we find that the electron mass gets largest around the field where the quasi-particle gap is closed. It is also shown that the induced moment of conduction electrons changes its direction from antiparallel to parallel to the field.
Magnetic correlations around the Mott transition in the Kagomé lattice Hubbard model
Takuma Ohashi,Sei-ichiro Suga,Norio Kawakami,Hirokazu Tsunetsugu
Physics , 2006, DOI: 10.1088/0953-8984/19/14/145251
Abstract: We study the magnetic properties around the Mott transition in the Kagom\'e lattice Hubbard model by the cellular dynamical mean field theory combined with quantum Monte Carlo simulations. By investigating the q-dependence of the susceptibility, we find a dramatic change of the dominant spin fluctuations around the Mott transition. The spin fluctuations in the insulating phase favor down to the lowest temperature a spatial spin configuration in which antiferromagnetic correlations are strong only in one chain direction but almost vanishing in the others.
Anomalous magnetic properties near Mott transition in Kagomé lattice Hubbard model
Takuma Ohashi,Sei-ichiro Suga,Norio Kawakami,Hirokazu Tsunetsugu
Physics , 2006, DOI: 10.1016/j.jmmm.2006.10.1143
Abstract: We investigate the characteristics of the metallic phase near the Mott transition in the Kagom\'e lattice Hubbard model using the cellular dynamical mean field theory. By calculating the specific heat and spin correlation functions, we demonstrate that the quasiparticles show anomalous properties in the metallic phase close to the Mott transition. We find clear evidence for the multi-band heavy quasiparticles in the specific heat, which gives rise to unusual temperature dependence of the spin correlation functions.
Magnetic properties of a Kondo insulator with RKKY interaction: Extended dynamical mean field study
Takuma Ohashi,Sei-ichiro Suga,Norio Kawakami
Physics , 2005, DOI: 10.1088/0953-8984/17/28/013
Abstract: We study the Kondo lattice model with the Heisenberg-type RKKY-exchange coupling among localized f-spins in the presence of a magnetic field. By means of an extended dynamical mean field theory combined with the non-crossing approximation, we investigate the one-particle spectral function and the dynamical spin correlation function in the Kondo insulating phase. It is shown that the magnetic field and the RKKY exchange interaction both cause the instability to the antiferromagnetic order with enhanced transverse spin fluctuations, which give rise to a strong renormalization of quasi-particles as the system approaches the quantum critical point. This leads to a tendency to retain the Kondo insulating gap up to rather large fields.
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