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AsIida, Kazuki*; Nagai, Yuki; Ishida, Shigeyuki*; Ishikado, Motoyuki*; Murai, Naoki; Christianson, A. D.*; Yoshida, Hiroyuki*; Inamura, Yasuhiro; Nakamura, Hiroki; Nakao, Akiko*; et al.
Physical Review B, 100(1), p.014506_1 - 014506_8, 2019/07
Times Cited Count：34 Percentile：84.94(Materials Science, Multidisciplinary)Magnetic excitations and magnetic structure of EuRbFeAs were investigated by neutron scattering measurements.
AsIida, Kazuki*; Ishikado, Motoyuki*; Nagai, Yuki; Yoshida, Hiroyuki*; Christianson, A. D.*; Murai, Naoki; Kawashima, Kenji*; Yoshida, Yoshiyuki*; Eisaki, Hiroshi*; Iyo, Akira*
Journal of the Physical Society of Japan, 86(9), p.093703_1 - 093703_4, 2017/09
Times Cited Count：23 Percentile：78.85(Physics, Multidisciplinary)
AsKodama, Katsuaki; Ishikado, Motoyuki*; Wakimoto, Shuichi; Kiho, Kunihiro*; Lee, C.-H.*; Iyo, Akira*; Eisaki, Hiroshi*; Shamoto, Shinichi
Physical Review B, 90(14), p.144510_1 - 144510_5, 2014/10
Times Cited Count：1 Percentile：4.64(Materials Science, Multidisciplinary)(As,P)Ishikado, Motoyuki; Kodama, Katsuaki; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Wakimoto, Shuichi; Iyo, Akira*; Eisaki, Hiroshi*; Arai, Masatoshi; Shamoto, Shinichi
Physica C, 471(21-22), p.643 - 646, 2011/11
Times Cited Count：4 Percentile：20.79(Physics, Applied)Superconducting gap symmetry of 
1111 system, which has the highest 
in iron-based superconductors, is considered to be full gap 
wave based on magnetic penetration depth and neutron scattering measurements. On the other hand, a line node gap symmetry is proposed in BaFe(As,P) based on magnetic penetration depth and thermal conductivity measurements despite comparatively its high- (=30 K). Inelastic neutron scattering of BaFe(As,P) may exhibit different magnetic excitations in the 
-position or 
-dependence of a resonant peak from that of La1111 system. In this study, we performed inelastic neutron scattering measurement on 36g polycrystalline powder sample of optimally-doped BaFe(As,P) using Fermi chopper spectrometer 4SEASONS in J-PARC. We will discuss about the possible superconducting gap symmetry based on our inelastic neutron scattering results.
Shamoto, Shinichi; Wakimoto, Shuichi; Kodama, Katsuaki; Ishikado, Motoyuki; Christianson, A. D.*; Lumsden, M. D.*; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Arai, Masatoshi; et al.
Physica C, 471(21-22), p.639 - 642, 2011/11
Times Cited Count：0 Percentile：0(Physics, Applied)We have studied low-energy spin excitations on polycrystalline LaFeAsO
F
samples by inelastic neutron scattering. The dynamical spin susceptibility 
''(
) of the superconducting samples is found to be comparable to that of the magnetically ordered parent sample. On the other hand, ''() almost vanishes at x=0.158, where the superconducting transition temperature T
is suppressed to 7 K. This suggests that the low energy spin excitations are closely connected with high-T superconductivity. The disappearance of the spin excitations at low energy would correspond to the disappearance of the hole Fermi surface as the electron concentration increases with doping, as observed in ARPES measurements of BaFe
CoAs
at x=0.15. The relationship between the spin excitation and the Fermi surface will be discussed in comparison with other iron-based superconductors.
-like spin resonance in the iron-based nodal superconductor BaFe(As
P
) observed using inelastic neutron scatteringIshikado, Motoyuki; Nagai, Yuki; Kodama, Katsuaki; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Wakimoto, Shuichi; Nakamura, Hiroki; Machida, Masahiko; Suzuki, Katsuhiro*; et al.
Physical Review B, 84(14), p.144517_1 - 144517_5, 2011/10
Times Cited Count：27 Percentile：70.58(Materials Science, Multidisciplinary)We performed inelastic neutron scattering on a powder sample of iron-based superconductor BaFe(AsP) with = 30 K. Although this system is expected to have line nodes in its superconducting order parameter, we have observed spin resonance at the same scattering vector as that appeared in the -wave iron-based superconductors without line nodes. Moreover, the resonance enhancement, which can be a measure of the area of sign reversal between the hole and electron Fermi surfaces (FSs), is comparable to those without line nodes. These facts indicate that the sign reversal between the FSs is still dominant in this system, and the line nodes should create only limited area of sign-reversal on a single FS. Hence the system can hold higher Tc than the other iron-based superconductors with nodal symmetry, such as LaFePO
and KFeAs (
10 K).
Fukuda, Tatsuo; Baron, A. Q. R.*; Nakamura, Hiroki; Shamoto, Shinichi; Ishikado, Motoyuki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; et al.
Physical Review B, 84(6), p.064504_1 - 064504_13, 2011/08
Times Cited Count：9 Percentile：39.24(Materials Science, Multidisciplinary)
; Comparison with LaFePONishi, Ichiro*; Ishikado, Motoyuki; Ideta, Shinichiro*; Malaeb, W.*; Yoshida, Teppei*; Fujimori, Atsushi*; Kotani, Yoshinori*; Kubota, Masato*; Ono, Kanta*; Yi, M.*; et al.
Physical Review B, 84(1), p.014504_1 - 014504_5, 2011/07
Times Cited Count：22 Percentile：65.59(Materials Science, Multidisciplinary)We have performed an angle-resolved photoemission spectroscopy (ARPES) study of the iron-based superconductor PrFeAsO and examined the Fermi surfaces and band dispersions near the fermi level. Heavily hole-doped electronic states have been observed due to the polar nature of the cleaved surfaces. Nevertheless, we have found that the ARPES spectra basically agree with band dispersions calculated in the local density approximation (LDA) if the bandwidth is reduced by a factor of 
2.5 and then the chemical potential is lowered by 70 meV. Comparison with previous ARPES results on LaFePO reveals that the energy positions of the 
- and 
-derived bands are considerably different between the two materials, which we attribute to the different pnictogen height as predicted by the LDA calculation.
Kodama, Katsuaki; Ishikado, Motoyuki; Esaka, Fumitaka; Iyo, Akira*; Eisaki, Hiroshi*; Shamoto, Shinichi
Journal of the Physical Society of Japan, 80(3), p.034601_1 - 034601_6, 2011/03
Times Cited Count：12 Percentile：60.38(Physics, Multidisciplinary) via inelastic X-ray scatteringFukuda, Tatsuo; Baron, A. Q. R.*; Nakamura, Hiroki; Shamoto, Shinichi; Ishikado, Motoyuki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; et al.
Journal of the Physical Society of Japan, 80(Suppl.B), p.SB015_1 - SB015_4, 2011/01
Times Cited Count：1 Percentile：11.3(Physics, Multidisciplinary)We have investigated phonons of PrFeAsO using high-resolution inelastic X-ray scattering and 
calculations. Extensive measurements show that there are some changes in phonon spectra with temperature and/or doping. However, we compare our data with several calculations and find that the experimentally observed changes are much smaller than differences between the experiment. data and the calculations. Agreement is improved if magnetism is included in the calculations. However, still in disagreement even in the parent sample below T
. We consider several modifications of the calculations. The best agreement is obtained from modifying the nonmagnetic calculation. by softening only the in-plane nearest-neighbor Fe-As force constant. Fluctuating magnetism may be a partial explanation for the failure of the calculations, but seems incomplete in the face of the similarity of the measured phonon response in all the systems investigated including those known to have static magnetism.
single crystals and its characterizationIshikado, Motoyuki; Shamoto, Shinichi; Kito, Hijiri*; Iyo, Akira*; Eisaki, Hiroshi*; Ito, Toshimitsu*; Tomioka, Yasuhide*
Physica C, 470(Suppl.1), p.S322 - S323, 2010/12
Times Cited Count：3 Percentile：17.12(Physics, Applied)Single crystals of oxygen deficient oxypnictide superconductor PrFeAsO have been grown by using belt-type anvil high pressure synthesis apparatus. Superconducting transition temperature (
) of the obtained single crystal is 45 K, and typical size is about 800 
1000 30 
. 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.
single crystalsOkazaki, Ryuji*; Konczykowski, M.*; Van der Beek, C. J.*; Kato, Tomonari*; Hashimoto, Kenichiro*; Shimozawa, Masaaki*; Shishido, Hiroaki*; Yamashita, Minoru*; Ishikado, Motoyuki; Kito, Hijiri*; et al.
Physica C, 470(Suppl.1), p.S485 - S486, 2010/12
Times Cited Count：0 Percentile：0(Physics, Applied)We report the lower critical fields 
measurements on Fe-based oxipnictide PrFeAsO single crystals for 
and 
-planes. To avoid the difficulty of determinations due to the flux pinning, we developed a novel method using a miniature hall-sensor array which can evaluate the local magnetic induction ai each sensor position. The hall sensor which is placed on the edge of the crystal clearly resolves the first flux penetration from the Meissner state. The temperature dependence of for is well scaled by the in-plane penetration depth and is consistent with a full-gap superconducting state. The anistropy of at low temperatures is estimated to be 3, which is much smaller than of 
. This indicates the multiband superconductivity, in which the active bands for superconductivity are more two-dimensional.
Van der Beek, C. J.*; Rizza, G.*; Konczykowski, M.*; Fertey, P.*; Monnet, I.*; Okazaki, Ryuji*; Kato, Tomonari*; Hashimoto, Kenichiro*; Shimozawa, Masaaki*; Shishido, Hiroaki*; et al.
Physica C, 470(Suppl.1), p.S385 - S386, 2010/12
Times Cited Count：1 Percentile：6.46(Physics, Applied)Crystalline disorder in the pnictide superconductor PrFeAsO is studied using magneto-optical visualisation of flux penetration, transmission electron microscopy, and X-ray diffraction using synchrotron radiation. Critical-state like flux distributions and the magnitude and temperature dependence of the critical current demonstrate bulk vortex pinning by oxygen vacancies at all temperatures.
Hirata, Yasuyuki*; Kojima, Kenji*; Uchida, Shinichi*; Ishikado, Motoyuki; Iyo, Akira*; Eisaki, Hiroshi*; Tajima, Setsuko*
Physica C, 470(Suppl.1), p.S44 - S46, 2010/12
Times Cited Count：2 Percentile：12.09(Physics, Applied)Infrared reflectivity spectra of the multilayered HgBaCa
Cu
O
(
= 2, 3, 4, and 5) are measured. Optical plasma modes associated with the Josephson coupling between CuO planes within a multilayer appear below 
in the c-axis component of the reflectivity spectrum. For the bilayer and trilayer compound an optical Josephson plasma mode appears at unprecedentedly high frequency, 700-800 cm
, below . The plasma frequencies appreciably decrease in four- and five-layer compounds which indicates the suppression of superconducting order in the inner CuO planes, consistent with the result of NMR experiment.
F
Shamoto, Shinichi; Ishikado, Motoyuki; Christianson, A. D.*; Lumsden, M. D.*; Wakimoto, Shuichi; Kodama, Katsuaki; Iyo, Akira*; Arai, Masatoshi
Physical Review B, 82(17), p.172508_1 - 172508_4, 2010/11
Times Cited Count：42 Percentile：81.29(Materials Science, Multidisciplinary)An optimally doped iron-based superconductor LaFeAsOF with T=29 K has been studied by inelastic powder neutron scattering. The magnetic excitation at Q = 1.15 
is enhanced below T, leading to a peak at E
=13 meV as the resonance mode.
Jarrige, I.; Ishii, Kenji; Yoshida, Masahiro; Fukuda, Tatsuo; Ikeuchi, Kazuhiko*; Ishikado, Motoyuki*; Hiraoka, Nozomu*; Tsuei, K.-D.*; Kito, Hijiri*; Iyo, Akira*; et al.
Physica C, 470(Suppl.1), p.S377 - S378, 2010/10
Times Cited Count：4 Percentile：21.9(Physics, Applied)FWakimoto, Shuichi; Kodama, Katsuaki; Ishikado, Motoyuki; Matsuda, Masaaki; Kajimoto, Ryoichi; Arai, Masatoshi; Kakurai, Kazuhisa; Esaka, Fumitaka; Iyo, Akira*; Kito, Hijiri*; et al.
Journal of the Physical Society of Japan, 79(7), p.074715_1 - 074715_4, 2010/07
Times Cited Count：50 Percentile：86.18(Physics, Multidisciplinary) single crystalKashiwaya, Hiromi*; Shirai, Kazumi*; Matsumoto, Tetsuro*; Shibata, Hajime*; Kambara, Hiroshi*; Ishikado, Motoyuki; Eisaki, Hiroshi*; Iyo, Akira*; Shamoto, Shinichi; Kurosawa, Itaru*; et al.
Applied Physics Letters, 96(20), p.202504_1 - 202504_3, 2010/05
Times Cited Count：28 Percentile：71.36(Physics, Applied)The 
-axis transport properties of a high-pressure synthesized PrFeAsO single crystal are studied using s-shaped junctions. Resistivity anisotropy of about 120 detected at 50 K shows the presence of strong anisotropy in the electronic states. The obtained critical current density for the -axis of 2.9 10
A/cm
is two orders of magnitude larger than that in BiSr
La
CuO
. The appearance of a hysteresis in the current-voltage curve below 
is the manifestation of the intrinsic Josephson effect similar to that in cuprate superconductors. The suppression of the critical current-normal resistance (
) product is explained by an inspecular transport in 
-wave pair potential.
and NdFeAsOF
superconducting crystalsVan der Beek, C. J.*; Rizza, G.*; Konczykowski, M.*; Fertey, P.*; Monnet, I.*; Klein, T.*; Okazaki, Ryuji*; Ishikado, Motoyuki; Kito, Hijiri*; Iyo, Akira*; et al.
Physical Review B, 81(17), p.174517_1 - 174517_11, 2010/05
Times Cited Count：98 Percentile：93.75(Materials Science, Multidisciplinary)Local magnetic measurements are used to quantitatively characterize heterogeneity and flux line pinning in PrFeAsO and NdFeAs(O,F)superconducting single crystals. In spite of spatial fluctuations of the critical current density on the macroscopic scale, it is shown that the major contribution comes from collective pinning of vortex lines by microscopic defects by the mean-free path fluctuation mechanism. The defect density extracted from experiment corresponds to the dopant atom density, which means that dopant atoms play an important role both in vortex pinning and in quasi-particle scattering.
FeAsO ( = La and Nd) obtained from charge transport experimentsIshida, Shigeyuki*; Nakajima, Masamichi*; Tomioka, Yasuhide*; Ito, Toshimitsu*; Miyazawa, Kiichi*; Kito, Hijiri*; Lee, C.-H.*; Ishikado, Motoyuki; Shamoto, Shinichi; Iyo, Akira*; et al.
Physical Review B, 81(9), p.094515_1 - 094515_6, 2010/03
Times Cited Count：21 Percentile：64.58(Materials Science, Multidisciplinary)Characteristic normal-state charge transport is found in the oxygen-deficient iron-arsenides FeAsO (: La and Nd) with the highest 's among known Fe-based superconductors. The effect of "doping" in this system is mainly on the carrier scattering, quite distinct from that in high- cuprates. In the superconducting regime of the La system with maximum = 28 K, the low-temperature resistivity is dominated by a term. On the other hand, in the Nd system with higher than 40 K, the carriers are subject to stronger scattering showing -linear resistivity and small magnetoresistance. Such strong scattering appears crucial for high- superconductivity in the iron-based system.
