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Zhang, D.*; Hu, X.*; Chen, T.*; Abernathy, D. L.*; 梶本 亮一; 中村 充孝; 古府 麻衣子; Foley, B. J.*; Yoon, M.*; Choi, J. J.*; et al.
Physical Review B, 102(22), p.224310_1 - 224310_10, 2020/12
The long carrier lifetime and defect tolerance in metal halide perovskites (MHPs) are major contributors to the superb performance of MHP optoelectronic devices. Large polarons were reported to be responsible for the long carrier lifetime. Yet microscopic mechanisms of the large polaron formation, including the so-called phonon melting, are still under debate. Here, time-of-flight inelastic neutron scattering experiments and first-principles density-functional theory calculations were employed to investigate the lattice vibrations (or phonon dynamics) in methylammonium lead iodide, a prototypical example of MHPs. Our findings are that optical phonons lose temporal coherence gradually with increasing temperature which vanishes at the orthorhombic-to-tetragonal structural phase transition. Surprisingly, however, we found that the spatial coherence is still retained throughout the decoherence process. We argue that the temporally decoherent and spatially coherent vibrations contribute to the formation of large polarons in this metal halide perovskite.
佐藤 研太朗*; 池内 和彦*; 梶本 亮一; 脇本 秀一; 新井 正敏*; 藤田 全基*
Journal of the Physical Society of Japan, 89(11), p.114703_1 - 114703_7, 2020/11
被引用回数:0To elucidate the spin dynamics of LaSr
CuO
, which couples with the charge degree of freedom, the spin excitations spanning the characteristic energy (
35--40 meV) are investigated for underdoped
= 0.10 and optimally doped (OP)
= 0.16 through inelastic neutron scattering measurements. Analysis based on a two-component picture of high-quality data clarified the possible coexistence of upright standing incommensurate (IC) excitations with gapless commensurate (C) excitations in the energy-momentum space. The IC component weakens the intensity toward
with increasing energy transfer (
), whereas the C component strengthens at high-
regions. The analysis results imply that the superposition of two components with a particular intensity balance forms an hourglass-shaped excitation in appearance. Furthermore, the temperature dependence of the intensity of each component exhibits different behaviors; the IC component disappears near the pseudo-gap temperature (
) upon warming, whereas the C component is robust against temperature. These results suggest the itinerant electron spin nature and the localized magnetism of the parent La
CuO
in IC and C excitations, respectively, similar to the spin excitations in the OP YBa
Cu
O
and HgBa
CuO
with higher superconducting-transition temperatures.
梶本 亮一; 中村 充孝; 飯田 一樹*; 蒲沢 和也*; 池内 和彦*; 稲村 泰弘; 石角 元志*
Journal of Neutron Research, 22(2-3), p.99 - 107, 2020/10
The elastic energy resolution, integrated intensity, and peak intensity of the direct-geometry neutron chopper spectrometer 4SEASONS at Japan Proton Accelerator Research Complex (J-PARC) were re-investigated. This was done with respect to the incident energy and the rotation speed of the Fermi chopper using incoherent scattering of vanadium and simple analytical formulas. The model calculations reproduced the observed values satisfactorily. The present work should be useful for estimating in instrument performance in experiments.
高濱 隆成*; 石井 透依*; 犬童 代梧*; 有薗 実駿*; 寺倉 千恵子*; 十倉 好紀*; 竹下 直*; 野田 正亮*; 桑原 英樹*; 斎木 琢夫*; et al.
Physical Review Materials (Internet), 4(7), p.074401_1 - 074401_11, 2020/07
被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)We investigated the structural, magnetic, transport, and high-temperature thermoelectric properties of single crystals of the pseudobrookite AlTi
O
for
grown using a floating zone. We found a correlation of spin-singlet Ti
-Ti
dimers coupled with the lattice even in the conductive
and
phases which develops with increasing
. This developing dimer correlation reduces the number of unpaired Ti
ions, which makes the compound more conductive owing to the suppression of disorder for
up to about 0.75. The dimer fluctuation causes a critical enhancement of the magnetic susceptibility at around 150 K in the
phase near the boundary (
) between the
and the
phases. Such a correlation of the spin-singlet Ti
-Ti
dimers may produce a high Seebeck coefficient in the conductive
and
phases leading to a large thermoelectric power factor at high temperatures.
Bao, S.*; Cai, Z.*; Si, W.*; Wang, W.*; Wang, X.*; Shangguan, Y.*; Ma, Z.*; Dong, Z.-Y.*; 梶本 亮一; 池内 和彦*; et al.
Physical Review B, 101(21), p.214419_1 - 214419_8, 2020/06
被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)We perform thermodynamic and inelastic neutron scattering (INS) measurements to study the lattice dynamics (phonons) of a cubic collinear antiferromagnet CuTeO
which hosts topological spin excitations (magnons). While the specific heat and thermal conductivity results show that the thermal transport is dominated by phonons, the deviation of the thermal conductivity from a pure phononic model indicates that there is a strong coupling between magnons and phonons. In the INS measurements, we find a mode in the excitation spectra at 4.5 K, which exhibits a slight downward dispersion around the Brillouin zone center. This mode disappears above the N
el temperature and thus cannot be a phonon. Furthermore, the dispersion is distinct from that of a magnon. Instead, it can be explained by the magnon-polaron mode, collective excitations resulting from the hybridization between magnons and phonons. We consider the suppression of the thermal conductivity and emergence of the magnon-polaron mode to be evidence for magnon-phonon coupling in Cu
TeO
.
飯田 一樹*; 古府 麻衣子; 鈴木 雄大*; 村井 直樹; 河村 聖子; 梶本 亮一; 稲村 泰弘; 石角 元志*; 長谷川 舜介*; 増田 隆嗣*; et al.
Journal of the Physical Society of Japan, 89(5), p.053702_1 - 053702_5, 2020/05
被引用回数:2 パーセンタイル:14.51(Physics, Multidisciplinary)We investigated the low-energy incommensurate (IC) magnetic fluctuations in SrRuO
by the high-resolution inelastic neutron scattering measurements and random phase approximation (RPA) calculations. We observed a spin resonance with energy of
meV centered at a characteristic wavevector
. The resonance energy corresponds well to the superconducting gap 2
= 0.56 meV estimated by the tunneling spectroscopy. The spin resonance shows the
modulation with a maximum at around
. The
modulated intensity of the spin resonance and our RPA calculations indicate that the superconducting gaps regarding the quasi-one-dimensional
and
sheets at the Fermi surfaces have the horizontal line nodes. These results may set a strong constraint on the pairing symmetry of Sr
RuO
. We also discuss the implications on possible superconducting order parameters.
目時 直人; Aczel, A. A.*; 青木 大*; Chi, S.*; Fernandez-Baca, J. A.*; Griveau, J.-C.*; 萩原 正人*; Hong, T.*; 芳賀 芳範; 池内 和彦*; et al.
JPS Conference Proceedings (Internet), 30, p.011123_1 - 011123_6, 2020/03
希土類(4)やアクチノイド(5
)は、電子数の増加とともに複雑さを増し、様々な相互作用が競合して多様な状態が出現する。多体
電子系の結晶場分裂はバンド幅より狭いため、(1)高分解能の実験が必要で、(2)遍歴的なCeやU化合物は本質的に明瞭なスペクトルを示さない。また、(3)国際規制物質NpやPuなど超アクチノイド元素の取り扱いは厳しく規制されている。そこで比較的局在性の強い物質や希土類関連物質の、中性子散乱実験による磁気励起の研究が有益である。本稿では重い電子系化合物NpPd
Al
と関連物質の
電子状態について述べる。
Xu, Z.*; Dai, G.*; Li, Y.*; Yin, Z.*; Rong, Y.*; Tian, L.*; Liu, P.*; Wang, H.*; Xing, L.*; Wei, Y.*; et al.
npj Quantum Materials (Internet), 5(1), p.11_1 - 11_7, 2020/02
被引用回数:2 パーセンタイル:26.75(Materials Science, Multidisciplinary)We use neutron scattering to study Vanadium (hole)-doped LiFeV
As. In the undoped state, LiFeAs exhibits superconductivity at
K and transverse incommensurate spin excitations similar to electron overdoped iron pnictides. Upon Vanadium doping to form LiFe
V
, the transverse incommensurate spin excitations in LiFeAs transform into longitudinally elongated ones in a similar fashion to that of potassium (hole)-doped Ba
K
Fe
As
but with dramatically enhanced magnetic scattering and elimination of superconductivity. This is different from the suppression of the overall magnetic excitations in hole-doped BaFe
As
and the enhancement of superconductivity near optimal hole doping. These results are consistent with density function theory plus dynamic mean field theory calculations, suggesting that Vanadium doping in LiFeAs may induce an enlarged effective magnetic moment
with a spin crossover ground state arising from the inter-orbital scattering of itinerant electrons.
出田 真一郎*; 村井 直樹; 中島 正道*; 梶本 亮一; 田中 清尚*
Physical Review B, 100(23), p.235135_1 - 235135_7, 2019/12
被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)BaK
Fe
As
has an exotic physical property where that the C
-SDW phase suddenly changes to the C
-magnetic phase and superconductivity is suppressed within a narrow composition range around x = 0.25. We have investigated the doping dependence of the electronic structure of Ba
K
Fe
As
using angle-resolved photoemission spectroscopy (ARPES) and found an anomaly in the superconducting (SC) gap structure only for x = 0.25 in both the hole and electron Fermi surfaces (FSs). We also propose that the mechanism of a newly observed double-resonance peak by inelastic neutron scattering is understandable by the SC gap obtained by ARPES. Our discovery reveals the important relationship between the C
- magnetic phase and superconductivity, and provides an opportunity to survey the underlying relationship between the SC gap and resonance mode in the hole-doped iron-based superconductor.
梶本 亮一; 中島 健次; 藤田 全基*; 石角 元志*; 鳥居 周輝*; 石川 喜久*; Miao, P.*; 神山 崇*
Journal of the Physical Society of Japan, 88(11), p.114602_1 - 114602_6, 2019/11
被引用回数:0 パーセンタイル:100(Physics, Multidisciplinary)A high-resolution time-of-flight powder neutron diffraction study of the layered nickel oxide PrSr
NiO
with
and
was performed to characterize the crystal structures of these highly hole-doped nickelates. For the sample with
, the Ni-O bond lengths decrease uniformly with decreasing temperature, and the atomic displacement parameters are similar to those for
. In contrast, for the sample with
, the out-of-plane Ni-O bond length shows a sharp thermal contraction in the high-temperature region, which is suggestive of changes in the orbital occupation accompanied by the development of checkerboard-type charge correlations. Furthermore, the
sample is characterized by a large atomic displacement parameter for the apical O atoms along the out-of-plane direction, which is interpreted as the existence of two types of Ni
sites with different orbital occupancies. The distinct difference between the
sample and the lower-concentration compounds should be related to the development of checkerboard-type charge ordering in the metallic matrix and possible orbital ordering at the Ni
sites at
in the hole-doped layered nickel oxides.
石角 元志*; 樹神 克明; 梶本 亮一; 中村 充孝; 稲村 泰弘; 池内 和彦*; Ji, S.*; 新井 正敏*; 社本 真一
Condensed Matter (Internet), 4(3), p.69_1 - 69_10, 2019/09
中性子非弾性散乱により観測された磁気共鳴モードのQ依存性という初めての手法で、FeTeSe
の超伝導対称性がs
波であることを実験的に示した。
梶本 亮一; 横尾 哲也*; 中村 充孝; 川北 至信; 松浦 直人*; 遠藤 仁*; 瀬戸 秀紀*; 伊藤 晋一*; 中島 健次; 河村 聖子
Physica B; Condensed Matter, 562, p.148 - 154, 2019/06
被引用回数:3 パーセンタイル:60.07(Physics, Condensed Matter)Seven time-of-flight quasielastic/inelastic neutron scattering instruments are installed on six beamlines in the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (JPARC). Four of these instruments are chopper-type direct-geometry spectrometers, one is a near-backscattering indirect-geometry spectrometer, and the other two are spin-echo-type spectrometers. This paper reviews the characteristic features, recent scientific outcomes, and progress in development of MLF spectrometers.
梶本 亮一; 石角 元志*; 吉良 弘*; 金子 耕士; 中村 充孝; 蒲沢 和也*; 稲村 泰弘; 池内 和彦*; 飯田 一樹*; 村井 直樹; et al.
Physica B; Condensed Matter, 556, p.26 - 30, 2019/03
被引用回数:2 パーセンタイル:60.07(Physics, Condensed Matter)Magnets are important for studying magnetism and are commonly used as sample environment devices of neutron scattering instruments. However, the use of magnets was prevented at the time-of-flight direct-geometry neutron spectrometer 4SEASONS in Materials and Life Science Experimental Facility (MLF) at J-PARC, because the instrument is surrounded by iron components, and it is equipped with a piece of equipment operated with magnetic bearings. In the present work, we investigate the influence of stray magnetic fields from a superconducting magnet which is shared among neutron scattering instruments in MLF. Based on the investigation, we modified 4SEASONS such that it can be used with the magnet. Finally, we successfully performed the first inelastic neutron scattering experiments with applied magnetic fields using this sample environment.
中島 健次; Harjo, S.; 山田 悟史*; 及川 健一; 梶本 亮一
JAEA-Review 2018-032, 43 Pages, 2019/02
大強度陽子加速器施設(J-PARC)物質・生命科学実験施設(MLF)では2017年より「MLF将来計画技術検討会」が設置され、MLFの線源や実験装置の将来計画について議論が行われてきた。同検討会では中性子実験装置についても装置カテゴリ毎に現状の問題点や今後目指すべき方向性についての報告がなされた。本報告書は、今後の将来計画の検討の一助とするべく、同検討会におけるMLF中性子実験装置に関する発表資料をまとめたものである。
飯田 一樹*; 吉田 紘行*; 岡部 博孝*; 片山 尚幸*; 石井 裕人*; 幸田 章宏*; 稲村 泰弘; 村井 直樹; 石角 元志*; 門野 良典*; et al.
Scientific Reports (Internet), 9(1), p.1826_1 - 1826_9, 2019/02
被引用回数:1 パーセンタイル:65.14(Multidisciplinary Sciences)Molecular based spin-1/2 triangular lattice systems have attracted research interest. LiMo
O
(
= In or Sc) is such a compound where spin-1/2 Mo
O
clusters in place of Mo ions form the uniform triangular lattice. Here, we report exotic magnetisms in Li
InMo
O
and Li
ScMo
O
investigated by muon spin rotation (
SR) and inelastic neutron scattering (INS) spectroscopies. Li
InMo
O
exhibits spin wave excitation which is quantitatively described by the nearest neighbor anisotropic Heisenberg model based on the 120
spin structure. In contrast, Li
ScMo
O
undergoes short-range magnetic order below 4 K with quantum-spin-liquid-like magnetic fluctuations down to the base temperature. Origin of the different ground states is discussed in terms of anisotropies of crystal structures and magnetic interactions.
梶本 亮一; 横尾 哲也*; 松浦 直人*
JAEA-Review 2018-024, 78 Pages, 2019/01
平成30年10月11日、MLF中性子分光器による合同のユーザーミーティング「DIRECTION 2018」がJ-PARC MLF、高エネルギー加速器研究機構物質構造科学研究所、総合科学研究機構の共催で開催された。本ミーティングは6つの分光器、すなわちBL01(4SEASONS)、BL02(DNA)、BL06(VIN ROSE)、BL12(HRC)、BL14(AMATERAS)、BL23(POLANO)におけるユーザー利用の活性化およびユーザーと装置の協力関係の構築を目指して開催されたものである。研究会では14件の口頭発表および21件のポスター発表が行われ、各装置を利用して行われた研究成果の紹介、各装置や試料環境に関する現状の報告がなされるとともに、装置や試料環境に関する要望や今後の展開等について密接な議論が交わされた。本報告書はこのミーティングの講演要旨および講演で使用された発表資料を収録したものである。
中島 健次; 梶本 亮一
Physica B; Condensed Matter, 551, p.142 - 145, 2018/12
被引用回数:0 パーセンタイル:100(Physics, Condensed Matter)We will report on magnetic excitations in lightly oxygen doped lanthanum nickel oxide, LaNiO
. By introducing slightly excessive oxygen atoms in the system, magnetic excitations in La
NiO
drastically changes its picture. In lower energy region, spin-wave stiffness strongly suppressed. On the other hand, in the higher energy region, spin-wave dispersion curve is almost same as in the stoichiometric system, while excitations show considerable broadening. Alternation of the character of the excitations by changing energy is also reported in hole doped cuprates and cobalates. We consider that this behavior is one of key clues to understand magnetism and transport properties in carrier doped layered transition metal oxides. We investigated detail of magnetic excitations in two different lightly doped systems, La
NiO
and La
NiO
in wide momentum and energy transfer space by using time-of-flight spectrometers at J-PARC. Observed doping effects in magnetic excitations will be discussed by comparing them to those reported in other related layered transition metal oxides.
中村 充孝; 神原 理*; 飯田 一樹*; 梶本 亮一; 蒲沢 和也*; 池内 和彦*; 石角 元志*; 青山 和弘*
Physica B; Condensed Matter, 551, p.480 - 483, 2018/12
被引用回数:1 パーセンタイル:87.78(Physics, Condensed Matter)近年、磁場や圧力、高温といった特殊環境下での中性子非弾性散乱実験へのニーズが高まっており、質の高いデータを得るためには試料環境機器からの不要な散乱をできる限り低く抑える必要がある。そこで、我々はユーザーのニーズに応えるため、J-PARCのフェルミチョッパー分光器四季に特化した揺動型ラジアルコリメータを開発した。四季では比較的高い入射エネルギーを用いることから、コリメータのブレード素材に水素フリーの金属シートを採用した。このラジアルコリメータの制御システムでは、揺動スピードや揺動角等といった揺動パターンを柔軟に変更することが可能である。本稿では、新たに開発したラジアルコリメータの性能と残された課題について報告する。
石角 元志*; 社本 真一; 樹神 克明; 梶本 亮一; 中村 充孝; Hong, T.*; Mutka, H.*
Scientific Reports (Internet), 8, p.16343_1 - 16343_6, 2018/11
被引用回数:2 パーセンタイル:61.53(Multidisciplinary Sciences)磁気揺らぎはBCS理論に従わない非従来型超伝導で最も可能性のある機構として重要な役割を担うと考えられてきた。今回、これまで磁気ゆらぎが見つかっていない5Kという低い超伝導転移温度の鉄リン系超伝導体LaFePOで、30-50meVの高エネルギーで磁気ゆらぎを見つけた。これはこれまで考えられてきた高エネルギー磁気揺らぎで、高い超伝導転移温度になるという考えとは矛盾することから、超伝導機構の理解に向けて重要な発見である。
池内 和彦*; 中島 健次; 河村 聖子; 梶本 亮一; 脇本 秀一; 鈴木 謙介*; 藤田 全基*
AIP Advances (Internet), 8(10), p.101318_1 - 101318_5, 2018/10
被引用回数:0 パーセンタイル:100(Nanoscience & Nanotechnology)中性子散乱実験により、Al不純物を導入した実効ホール濃度0.25の銅酸化物超伝導体、LaSr
Cu
Al
O
の巨大単結晶について、磁気励起を測定した。