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Journal Articles

Spin resonance in the new-structure-type iron-based superconductor CaKFe$$_{4}$$As$$_{4}$$

Iida, 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:22 Percentile:83.13(Physics, Multidisciplinary)

Journal Articles

Spontaneous decays of magneto-elastic excitations in non-collinear antiferromagnet (Y,Lu)MnO$$_{3}$$

Oh, J.*; Le, M. D.*; Nahm, H.-H.*; Sim, H.*; Jeong, J.*; Perring, T. G.*; Woo, H.*; Nakajima, Kenji; Kawamura, Seiko; Yamani, Z.*; et al.

Nature Communications (Internet), 7, p.13146_1 - 13146_6, 2016/10

 Times Cited Count:42 Percentile:84.65(Multidisciplinary Sciences)

Magnons and phonons are fundamental quasiparticles in a solid and can be coupled together to form a hybrid quasi-particle. However, detailed experimental studies on the underlying Hamiltonian of this particle are rare for actual materials. Moreover, the anharmonicity of such magnetoelastic excitations remains largely unexplored, although it is essential for a proper understanding of their diverse thermodynamic behaviour and intrinsic zero-temperature decay. Here we show that in non-collinear antiferromagnets, a strong magnon phonon coupling can significantly enhance the anharmonicity, resulting in the creation of magnetoelastic excitations and their spontaneous decay. By measuring the spin waves over the full Brillouin zone and carrying out anharmonic spin wave calculations using a Hamiltonian with an explicit magnon phonon coupling, we have identified a hybrid magnetoelastic mode in (Y,Lu)MnO$$_{3}$$ and quantified its decay rate and the exchange-striction coupling termrequired to produce it.

Journal Articles

Anisotropic magnetic form factor in a detwinned single crystal of BaFe$$_2$$As$$_2$$

Kodama, 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:5.23(Materials Science, Multidisciplinary)

Journal Articles

Inelastic neutron scattering on iron-based superconductor BaFe$$_2$$(As,P)$$_2$$

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:22.18(Physics, Applied)

Superconducting gap symmetry of $$Ln$$1111 system, which has the highest $$T_c$$ in iron-based superconductors, is considered to be full gap $$s_{pm}$$ wave based on magnetic penetration depth and neutron scattering measurements. On the other hand, a line node gap symmetry is proposed in BaFe$$_2$$(As,P)$$_2$$ based on magnetic penetration depth and thermal conductivity measurements despite comparatively its high-$$T_c$$ ($$T_c$$=30 K). Inelastic neutron scattering of BaFe$$_2$$(As,P)$$_2$$ may exhibit different magnetic excitations in the $$Q$$-position or $$E$$-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$$_2$$(As,P)$$_2$$ using Fermi chopper spectrometer 4SEASONS in J-PARC. We will discuss about the possible superconducting gap symmetry based on our inelastic neutron scattering results.

Journal Articles

Neutron scattering of iron-based superconductors

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$$_{1-x}$$F$$_{x}$$ samples by inelastic neutron scattering. The dynamical spin susceptibility $$chi$$''($$omega$$) of the superconducting samples is found to be comparable to that of the magnetically ordered parent sample. On the other hand, $$chi$$''($$omega$$) almost vanishes at x=0.158, where the superconducting transition temperature T$$_{c}$$ is suppressed to 7 K. This suggests that the low energy spin excitations are closely connected with high-T$$_{c}$$ 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$$_{2-x}$$Co$$_{x}$$As$$_{2}$$ at x=0.15. The relationship between the spin excitation and the Fermi surface will be discussed in comparison with other iron-based superconductors.

Journal Articles

$$s_{pm}$$-like spin resonance in the iron-based nodal superconductor BaFe$$_2$$(As$$_{0.65}$$P$$_{0.35}$$)$$_2$$ observed using inelastic neutron scattering

Ishikado, 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:26 Percentile:73.08(Materials Science, Multidisciplinary)

We performed inelastic neutron scattering on a powder sample of iron-based superconductor BaFe$$_2$$(As$$_{0.65}$$P$$_{0.35}$$)$$_2$$ with $$T_c$$ = 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 $$s_{pm}$$-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$$_{1-y}$$ and KFe$$_2$$As$$_2$$ ($$T_c <$$ 10 K).

Journal Articles

Soft and isotropic phonons in PrFeAsO$$_{1-y}$$

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:41.39(Materials Science, Multidisciplinary)

Journal Articles

Angle-resolved photoemission spectroscopy study of PrFeAsO$$_{0.7}$$; Comparison with LaFePO

Nishi, 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:66.92(Materials Science, Multidisciplinary)

We have performed an angle-resolved photoemission spectroscopy (ARPES) study of the iron-based superconductor PrFeAsO$$_{0.7}$$ 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 $$sim$$ 2.5 and then the chemical potential is lowered by $$sim$$ 70 meV. Comparison with previous ARPES results on LaFePO reveals that the energy positions of the $$d$$$$_{3z^{2}-r^{2}}$$- and $$d$$$$_{yz,zx}$$-derived bands are considerably different between the two materials, which we attribute to the different pnictogen height as predicted by the LDA calculation.

Journal Articles

Structural analysis on iron-based superconductor Pr1111 system with oxygen deficiency and flourine substitution

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:62.29(Physics, Multidisciplinary)

Journal Articles

From a single-band metal to a high-temperature superconductor via two thermal phase transitions

He, R.-H.*; Hashimoto, Makoto*; Karapetyan, H.*; Koralek, J. D.*; Hinton, J. P.*; Testaud, J. P.*; Nathan, V.*; Yoshida, Yoshiyuki*; Yao, H.*; Tanaka, Kiyohisa*; et al.

Science, 331(6024), p.1579 - 1583, 2011/03

 Times Cited Count:261 Percentile:98.8(Multidisciplinary Sciences)

The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature $$T^*$$ using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at $$T^*$$ of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature ($$T_c$$), entangled in an energy-momentum dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.

Journal Articles

Phonon spectra of PrFeAsO$$_{1-y}$$ via inelastic X-ray scattering

Fukuda, 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:11.83(Physics, Multidisciplinary)

We have investigated phonons of PrFeAsO$$_{1-y}$$ using high-resolution inelastic X-ray scattering and $$ab-initio$$ 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$$_N$$. We consider several modifications of the $$ab-initio$$ 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.

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

 Times Cited Count:4 Percentile:23.05(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

 Times Cited Count:3 Percentile:18.14(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

Lower critical fields and the anisotropy in PrFeAsO$$_{1-y}$$ single crystals

Okazaki, 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 $$H_{c1}$$ measurements on Fe-based oxipnictide PrFeAsO$$_{1-y}$$ single crystals for $$H$$ $$parallel$$ $$c$$ and $$H$$ $$parallel$$ $$ab$$-planes. To avoid the difficulty of $$H_{c1}$$ 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 $$H_{c1}$$ for $$H$$ $$parallel$$ $$c$$ is well scaled by the in-plane penetration depth and is consistent with a full-gap superconducting state. The anistropy of $$H_{c1}$$ at low temperatures is estimated to be $$sim$$ 3, which is much smaller than of $$H_{c2}$$. This indicates the multiband superconductivity, in which the active bands for superconductivity are more two-dimensional.

Journal Articles

Disorder and flux pinning in superconducting pnictide single crystals

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:6.88(Physics, Applied)

Crystalline disorder in the pnictide superconductor PrFeAsO$$_{1-x}$$ 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.

Journal Articles

Interlayer Josephson couplings in Hg-based multi-layered cuprates

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:12.75(Physics, Applied)

Infrared reflectivity spectra of the multilayered HgBa$$_{2}$$Ca$$_{n-1}$$Cu$$_{n}$$O$$_{2n+2+delta}$$ (${it n}$ = 2, 3, 4, and 5) are measured. Optical plasma modes associated with the Josephson coupling between CuO$$_{2}$$ planes within a multilayer appear below $$T$$$$_{rm c}$$ 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, $$sim$$ 700-800 cm$$^{-1}$$, below $$T$$$$_{rm c}$$. The plasma frequencies appreciably decrease in four- and five-layer compounds which indicates the suppression of superconducting order in the inner CuO$$_{2}$$ planes, consistent with the result of NMR experiment.

Journal Articles

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

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:23.05(Physics, Applied)

Journal Articles

Degradation of superconductivity and spin fluctuations by electron overdoping in LaFeAsO$$_{1-x}$$F$$_{x}$$

Wakimoto, 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:87.26(Physics, Multidisciplinary)

Journal Articles

C-axis critical current of a PrFeAsO$$_{0.7}$$ single crystal

Kashiwaya, 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:72.6(Physics, Applied)

The ${it c}$-axis transport properties of a high-pressure synthesized PrFeAsO$$_{0.7}$$ 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 ${it c}$-axis of 2.9 $$times$$ 10$$^{5}$$ A/cm$$^{2}$$ is two orders of magnitude larger than that in Bi$$_{2}$$Sr$$_{1.6}$$La$$_{0.4}$$CuO$$_{6+delta}$$. The appearance of a hysteresis in the current-voltage curve below ${it T}$ $$_{c}$$ is the manifestation of the intrinsic Josephson effect similar to that in cuprate superconductors. The suppression of the critical current-normal resistance (${it I}$ $$_{c}$$ ${it R}$ $$_{n}$$) product is explained by an inspecular transport in ${it s}$ $$_{pm}$$ -wave pair potential.

Journal Articles

Flux pinning in PrFeAsO$$_{0.9}$$ and NdFeAsO$$_{0.9}$$F$$_{0.1}$$ superconducting crystals

Van 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:93 Percentile:94.11(Materials Science, Multidisciplinary)

Local magnetic measurements are used to quantitatively characterize heterogeneity and flux line pinning in PrFeAsO$$_{1-y}$$ 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.

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