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Journal Articles

Low temperature structure of FeSr$$_{2}$$YCu$$_{2}$$O$$_{6+delta}$$ magnetic superconductor

Mochiku, Takashi*; Hata, Yoshiaki*; Wuernisha, T.*; Igawa, Naoki; Hoshikawa, Akinori*; Ishigaki, Toru*; Yasuoka, Hiroshi*; Hirata, Kazuto*

Physica C, 470(Suppl.1), p.S158 - S159, 2010/12

https://doi.org/10.1016/j.physc.2009.12.047
 Times Cited Count：2 Percentile：12.12(Physics, Applied)

We have performed neutron powder diffraction of the superconducting FeSr$$_{2}$$YCu$$_{2}$$O$$_{6+}$$$$_{delta}$$ and the nonsuperconducting FeSr$$_{2}$$Y(Cu$$_{0.95}$$Zn$$_{0.05}$$)$$_{2}$$O$$_{6+}$$$$_{delta}$$ samples at low temperature and room temperature to investigate the relation between the crystal structure ant the physical properties. Neutron diffraction study indicates that the magnetic order in this compound is not long-range order because we observed no extra reflection due to the magnetic superstructure. We have observed structural anomaly related to Cu in the superconducting sample around 30 K although we could not observe it in the nonsuperconducting sample. There is possibility of the change of the charge distribution around 30 K in the superconducting sample.

Journal Articles

Numerical exact diagonalization study on a phonon-assisted hole paring in the high-$$T_{rm c}$$ cuprates

Sakai, Toru

Physica C, 470(Suppl.1), p.S80 - S81, 2010/12

https://doi.org/10.1016/j.physc.2009.10.089
 Times Cited Count：0 Percentile：0(Physics, Applied)

In our previous study on the $$t-J$$-Holstein model including the breathing and buckling vibrations of the in-plane oxygen atoms, the suppression of hole pairing by the breathing mode was indicated, while the buckling mode was revealed to assist it. In the present study, we take the renormalization of the hole hopping parameter t due to the phonon effect into account and reconsider the phonon-assisted hole pairing mechanism. It is found that even the breathing vibration of in-plane oxygen can enhance the hole binding for some realistic parameters.

Journal Articles

Theoretical study of resonant inelastic X-ray scattering spectrum in the Hubbard ladder

Tsutsui, Kenji; Toyama, Takami*; Maekawa, Sadamichi*

Physica C, 470(Suppl.1), p.S232 - S233, 2010/12

https://doi.org/10.1016/j.physc.2009.10.042
 Times Cited Count：0 Percentile：0(Physics, Applied)

The spectra of the Cu $$K$$-edge Resonant inelastic X-ray scattering on the ladder cuprates are calculated by using the exact diagonalization method. So far it has been suggested that the momentum-dependence of the spectra on the ladder system is related with the formation of the spin singlet in the ground state. It has also revealed that the stabilization of the spin singlet strongly depends on the sign of the diagonal hopping of holes. In this study, in order to clarify the relationship between the spectra and the formation of the singlet state, the dependence of the spectra on the diagonal hopping of holes is examined. We find that the feature of the spectra is actually changed by the hopping and conclude that the resonant inelastic X-ray scattering can reveal the formation of the spin singlet state in the ladder system.

Journal Articles

Spin excitations in iron oxypnictide superconductor system

Shamoto, Shinichi; Ishikado, Motoyuki; Wakimoto, Shuichi; Kodama, Katsuaki; Kajimoto, Ryoichi; Arai, Masatoshi; Fukuda, Tatsuo; Nakamura, Hiroki; Machida, Masahiko; Eisaki, Hiroshi*

Physica C, 470(Suppl.1), p.S284 - S287, 2010/12

https://doi.org/10.1016/j.physc.2009.11.132
 Times Cited Count：4 Percentile：21.96(Physics, Applied)

Journal Articles

Resonant inelastic X-ray scattering of La$$_2$$Cu$$_{0.95}$$Ni$$_{0.05}$$O$$_4$$

Ishii, Kenji; Ikeuchi, Kazuhiko*; Jarrige, I.; Mizuki, Junichiro; Hiraka, Haruhiro*; Yamada, Kazuyoshi*; Tsutsui, Kenji; Toyama, Takami*; Maekawa, Sadamichi*; Endo, Yasuo*; et al.

Physica C, 470(Suppl.1), p.S155 - S157, 2010/12

https://doi.org/10.1016/j.physc.2009.11.171
 Times Cited Count：0 Percentile：0(Physics, Applied)

Journal Articles

Perturbation theory of iron-pnictide superconductivity

Nomura, Takuji

Physica C, 470(Suppl.1), p.S365 - S367, 2010/12

https://doi.org/10.1016/j.physc.2009.12.037
 Times Cited Count：0 Percentile：0(Physics, Applied)

The high-$$T_{rm c}$$ superconductivity in iron pnictides is studied within a perturbation theory. We employ a five-band Hubbard model taking account of five Fe3$$d$$-like local orbitals. The Eliashberg equation is solved by calculating the pairing interaction within the third-order perturbation expansion in the Coulomb interaction at iron sites. The superconducting order parameter changes sign between the disconnected Fermi surfaces, and the superconducting gap is fully opened without any nodes on the Fermi surface. The most favorable pairing symmetry is an $$s_pm$$-wave. It is suggested that the superconductivity disappears in high doping regions where the electron pockets or the hole pockets disappear.

Journal Articles

Inter-grain Josephson currents in two-gap superconductors

Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio*

Physica C, 470(Suppl.1), p.S489 - S490, 2010/12

https://doi.org/10.1016/j.physc.2009.11.016
 Times Cited Count：0 Percentile：0(Physics, Applied)

We microscopically study inter-grain Josephson current in iron-pnictide superconductors. The theoretical examination predicts that the inter-grain Josephson current is significantly reduced by $$pm s$$-wave symmetry as the incoherent tunneling process becomes dominant and the density of states and the gap amplitude between two bands are identical. In addition, we suggest important points to improve the inter-grain critical current density.

Journal Articles

Collective modes and Josephson vortices in a heterotic Josephson junction between single- and two-gap superconductors

Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio*; Matsumoto, Hideki*

Physica C, 470(Suppl.1), p.S882 - S883, 2010/12

https://doi.org/10.1016/j.physc.2009.10.023
 Times Cited Count：1 Percentile：6.48(Physics, Applied)

We construct a theory of a heterotic Josephson junction between single- and two-gap superconductors. The theory predicts the presence of in-phase and out-of-phase collective modes of superconducting phases. The former is the Josephson plasma mode, and the latter is a counterpart of Leggett's mode in Josephson junctions. A signature for $$pm s$$-wave superconductivity is a drastic reduction of the frequency of the Josephson plasma mode. We also show that the magnetic field distribution of the Josephson vortex for $$pm s$$-wave superconductivity is more enlarged than that for s-wave without sign change between the order parameters.

Journal Articles

Pressure effects on iron-based superconductors; A First-principles study

Nakamura, Hiroki; Machida, Masahiko

Physica C, 470(Suppl.1), p.S387 - S388, 2010/12

https://doi.org/10.1016/j.physc.2009.12.024
 Times Cited Count：1 Percentile：6.48(Physics, Applied)

Journal Articles

Magnetic structure and phonon spectra of iron-based superconductors; A First-principle study

Nakamura, Hiroki; Machida, Masahiko; Baron, A.*; Fukuda, Tatsuo; Shamoto, Shinichi

Physica C, 470(Suppl.1), p.S430 - S432, 2010/12

https://doi.org/10.1016/j.physc.2009.10.138
 Times Cited Count：1 Percentile：6.48(Physics, Applied)

Journal Articles

Phenomenological theory for $$pm$$s-wave superconducting states of iron-based superconductors

Machida, Masahiko; Nagai, Yuki*; Ota, Yukihiro; Nakai, Noriyuki; Nakamura, Hiroki; Hayashi, Nobuhiko*

Physica C, 470(Suppl.1), p.S372 - S374, 2010/12

https://doi.org/10.1016/j.physc.2009.10.087
 Times Cited Count：2 Percentile：12.12(Physics, Applied)

We briefly present three phenomenological theoretical works for superconducting properties in iron-based superconductors. The first is a suggestion of multi-band $$pm$$ s-wave pairing model consistently explaining different measurement data, the second a proposal to detect $$pm$$ s-wave signature, and the third an evaluation of the critical current in polycrystalline samples by considering $$pm$$ s-wave symmetry.

Journal Articles

Small jump of specific heat and small gap in iron pnictide superconductors

Nakai, Noriyuki; Nakamura, Hiroki; Ota, Yukihiro; Nagai, Yuki*; Hayashi, Nobuhiko*; Machida, Masahiko

Physica C, 470(Suppl.1), p.S368 - S369, 2010/12

https://doi.org/10.1016/j.physc.2010.01.055
 Times Cited Count：1 Percentile：6.48(Physics, Applied)

Journal Articles

Growth of PrFeAsO$$_{1-y}$$ single crystals and its characterization

Ishikado, Motoyuki; Shamoto, Shinichi; Kito, Hijiri*; Iyo, Akira*; Eisaki, Hiroshi*; Ito, Toshimitsu*; Tomioka, Yasuhide*

Physica C, 470(Suppl.1), p.S322 - S323, 2010/12

https://doi.org/10.1016/j.physc.2009.11.165
 Times Cited Count：3 Percentile：17.17(Physics, Applied)

Single crystals of oxygen deficient oxypnictide superconductor PrFeAsO$$_{1-y}$$ have been grown by using belt-type anvil high pressure synthesis apparatus. Superconducting transition temperature ($textit{T$_c$}$) of the obtained single crystal is 45 K, and typical size is about 800 $$times$$ 1000 $$times$$ 30 $$mu m^3$$. In-plane electrical resistivity shows almost proportional to temperature as well as the copper oxide high temperature superconductors, suggesting the existence of effects of strong inelastic scattering like copper oxide high temperature superconductor. In addition, we obtained non-superconducting parent single crystal by annealing the as-grown single crystal under ambient pressure. Resistivity of parent single crystal is characterized by the kink near 150 K corresponding to the structural transition, and the structure near 12 K, which is thought to be originating from the magnetic order of Pr ion.

Journal Articles

Dynamics of attractively interacting fermi atoms in one-dimensional optical lattices; Non-equilibrium simulations of fermi superfluidity

Okumura, Masahiko; Onishi, Hiroaki; Yamada, Susumu; Machida, Masahiko

Physica C, 470(Suppl.1), p.S949 - S951, 2010/12

https://doi.org/10.1016/j.physc.2009.11.178
 Times Cited Count：4 Percentile：21.96(Physics, Applied)

We study center of mass (CoM) motions of attractively interacting fermionic atoms loaded on an one-dimensional optical lattice confined by a harmonic potential at zero temperature by using adaptive time-dependent density-matrix renormalization-group method. We find that the CoM motions in weak and strong attraction show underdamped and overdamped motions, respectively, which are consistent with the experimental results of the CoM motion in the three-dimensional optical lattice. In addition, we find spin-imbalance effects on the CoM motion, which slow the CoM motion down.

Journal Articles

Density-matrix renormalization-group studies for one-dimensional polarized Anderson-Hubbard model

Okumura, Masahiko; Yamada, Susumu; Machida, Masahiko

Physica C, 470(Suppl.1), p.S952 - S954, 2010/12

https://doi.org/10.1016/j.physc.2009.11.003
 Times Cited Count：0 Percentile：0(Physics, Applied)

By using the density-matrix renormalization-group method, we study impurity effects on the pair correlation function of the one dimensional spin-imbalanced Anderson-Hubbard model. In strongly-attractive interacting cases in the presence of weak random potentials, we find that the Fulde-Ferrell-Larkin-Ovchinnikov type pair correlation function with nodes decays slower than that of Bardeen-Cooper-Schrieffer type one without nodes. This means that the former type pairing is unexpectedly more robust against randomness in the strong coupling regime.

Journal Articles

Effects of heavy-ion irradiation on the vortex state in Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$

Tamegai, Tsuyoshi*; Tsuchiya, Yuji*; Taen, Toshihiro*; Nakajima, Yasuyuki*; Okayasu, Satoru; Sasase, Masato*

Physica C, 470(Suppl.1), p.S360 - S362, 2010/12

https://doi.org/10.1016/j.physc.2009.11.051
 Times Cited Count：1 Percentile：6.48(Physics, Applied)

We report effects of heavy-ion irradiation in Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$ single crystals. The columnar defects with about 40% of the irradiation dose are confirmed by transmission electron microscopy. Magneto-optical imaging and bulk magnetization measurements reveal strong enhancement of the critical current density in the irradiated region. The vortex creep rate is also strongly suppressed by the columnar defects. Effects of heavy-ion irradiation into Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$ and cuprate superconductors are compared.

Oral presentation

Unusual magnetic field response in non-centrosymmetric heavy-fermion superconductor CePt$$_3$$Si

Kaneko, Koji; Stockert, O.*; Arndt, J.*; Borth, R.*; Skoulatos, M.*; Habicht, K.*; Kiefer, K.*; Schneidewind, A.*; Etzdorf, D.*; Takeuchi, Tetsuya*; et al.

no journal, , 

Oral presentation

Inelastic X-ray scattering studies of the phonon properties on iron-based new superconductors

Fukuda, Tatsuo; Baron, A. Q. R.*; Shamoto, Shinichi; Ishikado, Motoyuki; Nakamura, Hiroki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; et al.

no journal, , 

Oral presentation

Magnetic dispersion of the diagonal incommensurate phase in lightly-doped La$$_{2-x}$$Sr$$_x$$CuO$$_4$$

Matsuda, Masaaki; Fujita, Masaki*; Wakimoto, Shuichi; Fernandez-Baca, J. A.*; Tranquada, J. M.*; Yamada, Kazuyoshi*

no journal, , 

We performed inelastic neutron scattering experiments on almost single-domain crystals of lightly-doped La$$_{2-x}$$Sr$$_x$$CuO$$_4$$ ($$x$$=0.021 and 0.04). Despite the rotated incommensurability, we find that the spectrum in this insulating phase with a diagonal incommensurate spin modulation is consistent with the hour-glass dispersion observed in superconducting La$$_{2-x}$$Sr$$_x$$CuO$$_4$$ and YBa$$_2$$Cu$$_3$$O$$_{6+x}$$, where the spin modulation is bond parallel. In particular, we find that the energy at which the excitations cross the commensurate antiferromagnetic wave vector increases roughly linearly with doping through the underdoped regime.

Oral presentation

Resonant inelastic X-ray scattering in single-crystal superconducting PrFeAsO$$_{0.7}$$

Jarrige, I.; Ishii, Kenji; Fukuda, Tatsuo; Yoshida, Masahiro; Ikeuchi, Kazuhiko*; Ishikado, Motoyuki; Shamoto, Shinichi

no journal, , 

Oral presentation

Doping dependence of spin fluctuations in LaFeAsO$$_{1-x}$$F$$_{x}$$ superconductor studied by inelastic neutron scattering

Wakimoto, Shuichi; Kodama, Katsuaki; Ishikado, Motoyuki; Kajimoto, Ryoichi; Arai, Masatoshi; Kakurai, Kazuhisa; Iyo, Akira*; Kito, Hijiri*; Eisaki, Hiroshi*; Shamoto, Shinichi

no journal, , 

21 (Records 1-20 displayed on this page)