Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Okumura, Masahiko; Nakai, Noriyuki; Nakamura, Hiroki; Hayashi, Nobuhiko; Yamada, Susumu; Machida, Masahiko
Physica C, 469(15-20), p.932 - 935, 2009/10
Times Cited Count：8 Percentile：36.66(Physics, Applied)Recently the superconductor of LaFeAsO was found and it has attracted much attentions by both theorists and experimentalists. We studies the effective two-bands model proposed by Raghu et al. [arXiv:0804.1113] by parallelized density-matirx renormalization group method [S. Yamada, M. Okumura, and M. Machida, arXiv:0707.0159]. By using this method, we can evaluate strong correlation effects caused by not only on-site but also inter-band interactions. We discuss these effects on physical quantities. In addition, we plan to propose a two-bands model including inter-band interaction in the cold atom system, which related the effective model of LaFeAsO. This model enables us to study systematically effects of inter-bands interaction because many parameters can be controlled precisely in this system. We expect that this system is useful to understand some behaviors of LaFeAsO.
Nakai, Noriyuki; Hayashi, Nobuhiko; Machida, Masahiko
Physica C, 469(15-20), p.1106 - 1109, 2009/10
Times Cited Count：10 Percentile：42.43(Physics, Applied)We investigate the orientation of the vortex lattice driven by an applied current by means of numerical simulations based on the time-dependent Ginzburg-Landau (TDGL) theory. A lattice order is restored by a current driving of vortices under the influence of random vortex pinnings. The orientation of the moving vortex lattice is different between the presence and the absence of vortex pinnings. In the absence of vortex pinnings, the lattice vector is parallel to the direction of vortex motion. On the other hand, in the presence of vortex pinnings and in the collective vortex flow phase, we found that the lattice vector is perpendicular to the direction of vortex motion, which is consistent with the experimental observation under intermediate magnetic fields in an amorphous superconductor.
Nakamura, Hiroki; Hayashi, Nobuhiko; Nakai, Noriyuki; Machida, Masahiko
Physica C, 469(15-20), p.1024 - 1026, 2009/10
Times Cited Count：8 Percentile：33.2(Physics, Applied)We perform first-principle phonon calculations for three typical iron-based superconductors, i.e., LaFeAsO, BaFe
As, and FeSe. Though those crystals have different structures, we find that the optical modes associated with Fevibration have almost similar characters. Moreover, we examine the pressure effect on phonons in FeSe. By increasing the external pressure, the phonon mode frequency related to Fe vibration effectively rises up and the electronic density of states at Fermi level also increases. These results may correlate to the critical temperature enhancement under high pressure.
Nakamura, Hiroki; Hayashi, Nobuhiko; Nakai, Noriyuki; Okumura, Masahiko; Machida, Masahiko
Physica C, 469(15-20), p.908 - 911, 2009/10
Times Cited Count：25 Percentile：68.57(Physics, Applied)In order to resolve a discrepancy of the magnetic moment on Fe between the experimental and calculation results, we perform first-principle electronic structure calculations for iron-based superconductors LaFeAsO
F
in which 
and 
by using the LSDA+
framework. Consequently, we confirm in both the mother and doped compounds that negative correction is crucial in matching the calculated magnetic moment with the observed one. A reason of the negative correction is that the Coulomb interaction on Fe orbitals is unexpectedly screened than LSDA's expectation. We discuss which type of situation emerges when the negative is a good correction in these compounds.
and its characterizationIshikado, Motoyuki; Shamoto, Shinichi; Kito, Hijiri*; Iyo, Akira*; Eisaki, Hiroshi*; Ito, Toshimitsu*; Tomioka, Yasuhide*
Physica C, 469(15-20), p.901 - 904, 2009/10
Times Cited Count：23 Percentile：66.35(Physics, Applied)We have successfully grown single crystals of oxygen deficient oxypnictide superconductor PrFeAsO by belt-type anvil apparatus using high pressure synthesis method.
