Yoshiaki Ōno
Niigata University
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Featured researches published by Yoshiaki Ōno.
EPL | 2004
W. Koller; D. Meyer; Yoshiaki Ōno; A. C. Hewson
We investigate metal-insulator transitions in the half-filled Holstein-Hubbard model as a function of the on-site electron-electron interaction U and the electron-phonon coupling g. We use several different numerical methods to calculate the phase diagram, the results of which are in excellent agreement. When the electron-electron interaction U is dominant, the transition is to a Mott insulator; when the electron-phonon interaction dominates, the transition is to a localized bipolaronic state. In the former case, the transition is always found to be second order. This is in contrast to the transition to the bipolaronic state, which is clearly first order for larger values of U. We also present results for the quasiparticle weight and the double occupancy as functions of U and g.
Journal of the Physical Society of Japan | 2010
Yuki Yanagi; Youichi Yamakawa; Naoko Adachi; Yoshiaki Ōno
We investigate the 16-band d-p model for iron pnictide superconductors in the presence of the electron-phonon coupling g with the orthorhombic mode which is crucial for reproducing the recently observed ultrasonic softening. Within the RPA, we obtain the ferro-orbital order below TQ which induces the tetragonal-orthorhombic structural transition at Ts = TQ, together with the stripe-type antiferromagnetic order below TN. Near the phase transitions, the system shows the s++ wave superconductivity due to the orbital fluctuation for a large g case with TQ > TN, while the s+- wave due to the magnetic fluctuation for a small g case with TQ TN.
Journal of the Physical Society of Japan | 2016
Takemi Yamada; Kaoru Domon; Yoshiaki Ōno
The three-chain Hubbard model for Ta2NiSe5, known as a candidate material for an excitonic insulator, is investigated over the wide range of the energy gap D between the twofold degenerate conduction bands and the nondegenerate valence band including both semiconducting (D > 0) and semimetallic (D < 0) cases. In the semimetallic case, the difference in the band degeneracy inevitably causes the imbalance of each Fermi wavenumber, resulting in a remarkable excitonic state characterized by the condensation of excitons with finite center-of-mass momentum q, the so-called Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) excitonic state. With decreasing D corresponding to increasing pressure, the obtained excitonic phase diagram shows a crossover from BEC (\(D \gtrsim 0\)) to BCS (\(D \lesssim 0\)) regime, and then shows a distinct phase transition at a certain critical value Dc (< 0) from the uniform (q = 0) to the FFLO (q ≠ 0) excitonic state, as expected to be observed in Ta2NiSe5 under high pressure.
Journal of the Physical Society of Japan | 2009
Yoko Miura; Masatoshi Sato; Youichi Yamakawa; Tatsuro Habaguchi; Yoshiaki Ōno
A pseudo honeycomb system Li 2 RuO 3 exhibits a second-order-like transition at temperature T = T c ∼540 K to a low- T nonmagnetic phase with a significant lattice distortion forming Ru–Ru pairs. For this system, we have calculated the band structure, using the generalized gradient approximation (GGA) in both the high- and low- T phases, and found that the results of the calculation can naturally explain the insulating behavior observed in the low- T phase. The detailed characters of the Ru 4 d t 2g bands obtained by the tight-binding fit to the calculated dispersion curves show clear evidence that the structural transition is driven by the formation of the Ru–Ru molecular orbit, as proposed in our previous experimental studies.
Physical Review B | 2004
Kazuhiro Sano; Yoshiaki Ōno
The one-dimensional extended Hubbard model with both the on-site
Journal of the Physical Society of Japan | 2013
Taiji Chiba; Michiaki Matsukawa; Junki Tada; Satoru Kobayashi; M. Hagiwara; Tsuyoshi Miyazaki; Kazuhiro Sano; Yoshiaki Ōno; Takahiko Sasaki; J. Echigoya
U
Journal of the Physical Society of Japan | 2014
Takemi Yamada; Jun Ishizuka; Yoshiaki Ōno
and the nearest neighbor
Physica B-condensed Matter | 2005
W. Koller; D. Meyer; A. C. Hewson; Yoshiaki Ōno
V
Journal of the Physical Society of Japan | 2016
Jun Ishizuka; Takemi Yamada; Yuki Yanagi; Yoshiaki Ōno
interactions at quarter filling is studied by using a novel finite size scaling. We diagonalize finite size systems numerically and calculate the Luttinger-liquid parameter
Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013) | 2014
Jun Ishizuka; Takemi Yamada; Yuki Yanagi; Yoshiaki Ōno
K_{\rho}