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Journal Articles

Lattice dynamics in FeSe via inelastic X-ray scattering and first-principles calculations

Murai, Naoki; Fukuda, Tatsuo; Nakajima, Masamichi*; Kawamura, Mitsuaki*; Ishikawa, Daisuke*; Tajima, Setsuko*; Baron, A. Q. R.*

Physical Review B, 101(3), p.035126_1 - 035126_6, 2020/01

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

We report an inelastic X-ray scattering investigation of phonons in FeSe superconductor. Comparing the experimental phonon dispersion with density functional theory (DFT) calculations in the non-magnetic state, we found a significant disagreement between them. A better overall agreement was obtained by allowing for spin-polarization in DFT calculations, despite the absence of magnetic order in FeSe. This calculation gives a realistic approximation, at DFT level, of the disordered paramagnetic state of FeSe, in which strong spin fluctuations are present.

Journal Articles

Effect of magnetism on lattice dynamics in SrFe$$_2$$As$$_2$$ using high-resolution inelastic X-ray scattering

Murai, Naoki*; Fukuda, Tatsuo; Kobayashi, Tatsuya*; Nakajima, Masamichi*; Uchiyama, Hiroshi*; Ishikawa, Daisuke*; Tsutsui, Satoshi*; Nakamura, Hiroki; Machida, Masahiko; Miyasaka, Shigeki*; et al.

Physical Review B, 93(2), p.020301_1 - 020301_5, 2016/01

 Times Cited Count:6 Percentile:55.15(Materials Science, Multidisciplinary)

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:86.1(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

Momentum-resolved charge excitations in high-$$T$$$$_{rm c}$$ cuprates studied by resonant inelastic X-ray scattering

Ishii, Kenji; Hoesch, M.*; Inami, Toshiya; Kuzushita, Kaori*; Owada, Kenji; Tsubota, Masami; Murakami, Yoichi; Mizuki, Junichiro; Endo, Yasuo; Tsutsui, Kenji*; et al.

Journal of Physics and Chemistry of Solids, 69(12), p.3118 - 3124, 2008/12

 Times Cited Count:3 Percentile:79.94(Chemistry, Multidisciplinary)

Journal Articles

Momentum dependence of Mott gap excitations in optimally doped YBa$$_2$$Cu$$_3$$O$$_{7-delta}$$ studied by resonant inelastic X-ray scattering

Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Kuzushita, Kaori; Inami, Toshiya; Owada, Kenji; Maekawa, Sadamichi*; Masui, Takahiko*; Tajima, Setsuko*; et al.

AIP Conference Proceedings 850, p.445 - 446, 2006/09

Mott gap excitations in the optimally doped high-$$T_{c}$$ superconductor YBa$$_2$$Cu$$_3$$O$$_{7-delta}$$ ($$T_{c}$$ = 93 K) have been studied by the resonant inelastic X-ray scattering method. Anisotropic spectra in the $$ab$$-plane are observed in a twin-free crystal. The excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the $$b^{*}$$ direction, while the excitation from the CuO$$_2$$ plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard model reproduces the observed spectra when different values of the on-site Coulomb energy are assumed. The Mott gap of the CuO chain site is found to be much smaller than that of the CuO$$_2$$ plane site.

Journal Articles

Mott gap excitations in twin-free YBa$$_2$$Cu$$_3$$O$$_{7-delta}$$ ($$T_{c}$$ = 93 K) studied by resonant inelastic X-ray scattering

Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Kuzushita, Kaori; Inami, Toshiya; Owada, Kenji; Maekawa, Sadamichi*; Masui, Takahiko*; Tajima, Setsuko*; et al.

Physical Review Letters, 94(18), p.187002_1 - 187002_4, 2005/05

 Times Cited Count:38 Percentile:18.06(Physics, Multidisciplinary)

Mott gap excitations in the optimally doped high-$$T_{c}$$ superconductor YBa$$_2$$Cu$$_3$$O$$_{7-delta}$$ ($$T_{c}$$ = 93 K) have been studied by the resonant inelastic X-ray scattering method. Anisotropic spectra in the $$ab$$-plane are observed in a twin-free crystal. The excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the $$b^{*}$$ direction, while the excitation from the CuO$$_2$$ plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard model reproduces the observed spectra when different values of the on-site Coulomb energy are assumed. The Mott gap of the CuO chain site is found to be much smaller than that of the CuO$$_2$$ plane site.

Oral presentation

Resonant inelastic X-ray scattering in strongly correlated electron systems

Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Inami, Toshiya; Owada, Kenji; Kuzushita, Kaori*; Hoesch, M.; Tsubota, Masami; Mizuki, Junichiro; et al.

no journal, , 

Resonant inelastic X-ray scattering studies on high-$$T_c$$ superconductors Nd$$_{2-x}$$Ce$$_x$$CuO$$_4$$ and YBa$$_2$$Cu$$_3$$O$$_{6+x}$$ are presented. In Nd$$_2$$CuO$$_4$$ and YBa$$_2$$Cu$$_3$$O$$_6$$, which are Mott insulators, an excitation across the Mott gap is observed around 2 eV. The spectral weight of this excitation shifts to higher energy with increasing the momentum transfer and the dispersion of the excitation is larger along the $$[pi,pi]$$ direction than the $$[pi,0]$$ direction. An intraband excitation in the upper Hubbard band emerges in the spectra of electron-doped Nd$$_{1.85}$$Ce$$_{0.15}$$CuO$$_4$$. As a function of the momentum transfer in the CuO$$_2$$ plane, the excitation shifts to higher energy up to 2-2.5 eV at the zone boundary, accompanied by an increase of the spectral width. On the other hand, excitations from two inequivalent Cu sites in hole-doped YBa$$_2$$Cu$$_3$$O$$_7$$ are distinguished by the momentum dependence and the Mott gap of the CuO chain site is found to be much smaller than that of the CuO$$_2$$ plane site.

Oral presentation

Effect of magnetism on phonon dispersion of SrFe$$_2$$As$$_2$$ via inelastic X-ray scattering

Murai, Naoki*; Fukuda, Tatsuo; Uchiyama, Hiroshi*; Tsutsui, Satoshi*; Ishikawa, Daisuke*; Kobayashi, Tatsuya*; Nakamura, Hiroki; Machida, Masahiko; Nakajima, Masamichi*; Miyasaka, Shigeki*; et al.

no journal, , 

no abstracts in English

Oral presentation

Magneto-elastic coupling in detwinned Sr(Fe$$_{1-x}$$Co$$_x$$)$$_2$$As$$_2$$ by inelastic X-ray scattering

Murai, Naoki*; Fukuda, Tatsuo; Nakajima, Masamichi*; Kobayashi, Tatsuya*; Uchiyama, Hiroshi*; Tsutsui, Satoshi*; Ishikawa, Daisuke*; Nakamura, Hiroki; Machida, Masahiko; Miyasaka, Shigeki*; et al.

no journal, , 

Oral presentation

Effect of magnetism on lattice dynamics of SrFe$$_{2}$$As$$_{2}$$ via high-resolution inelastic X-ray scattering

Murai, Naoki; Fukuda, Tatsuo; Kobayashi, Tatsuya*; Nakajima, Masamichi*; Uchiyama, Hiroshi*; Ishikawa, Daisuke*; Tsutsui, Satoshi*; Nakamura, Hiroki; Machida, Masahiko; Miyasaka, Shigeki*; et al.

no journal, , 

We report the first IXS study of single crystals of SrFe$$_{2}$$As$$_{2}$$ that have been detwinned via application of in-plane uniaxial stress. Our results clearly show anisotropy in phonon structure below $$it T_{s}$$ = $$it T_{N}$$ characterized by mode splitting at tetragonally-equivalent momentum transfers. To the best of our knowledge, this is the first observation of phonon anisotropy in iron-pnictides at finite momentum transfers. We obtain good agreement with our results using calculations that are modified to account for a reduced magnetic moment and fluctuating magnetism. Previous efforts using either non-magnetic calculations or static magnetism tend to either get the dispersion wrong from non-magnetic calculations or strongly over-estimate the phonon mode splitting when static magnetism is included. Our model for the response below $$it T_{N}$$ incorporates a phenomenological reduction in force constant anisotropy, by about 65%, that can be attributed to residual fast magnetic fluctuations. Above $$it T_{N}$$, all fluctuations are assumed to be fast and the response becomes the average of the results from the static magnetism. This serves as a starting point for a general model of phonons in iron-pnictides applicable to both non-magnetic and magnetic phases.

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