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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.
Ghys, L.*; Andreyev, A. N.; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Capponi, L.*; Cocolios, T. E.*; Cubiss, J.*; Derkx, X.*; et al.
Physical Review C, 100(5), p.054310_1 - 054310_13, 2019/11
被引用回数:5 パーセンタイル:18.92(Physics, Nuclear)The aim of this work was to investigate the -decay properties of
Fr and daughter products. Neutron-deficient francium nuclei are produced at ISOLDE-CERN bombarding a UCx target with 1.4 GeV protons. Due to the very high statistics and the high beam purity, improved decay data for
Fr and its daughters were obtained. The observation of crossover transitions positioned the isomeric high-spin level of
At at an excitation energy of 265(3) keV. Half-life values of 4.47(5) s and 1.28(10) s were extracted for the ground state and isomeric state of
At and 52(3) ms for the ground-state decay of
Fr.
Barzakh, A. E.*; Cubiss, J. G.*; Andreyev, A. N.; Seliverstov, M. D.*; Andel, B.*; Antalic, S.*; Ascher, P.*; Atanasov, D.*; Beck, D.*; Biero, J.*; et al.
Physical Review C, 99(5), p.054317_1 - 054317_9, 2019/05
被引用回数:3 パーセンタイル:27.46(Physics, Nuclear)Hyperfine-structure parameters and isotope shifts for the 795-nm atomic transitions in At have been measured at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy technique. Magnetic dipole and electric quadrupole moments, and changes in the nuclear mean-square charge radii, have been deduced. A large inverse odd-even staggering in radii, which may be associated with the presence of octupole collectivity, has been observed. Namely, the radius of the odd-odd isotope
At has been found to be larger than the average.
Dioguardi, A. P.*; 安岡 弘志*; Thomas, S. M.*; 酒井 宏典; Cary, S. K.*; Kozimor, S. A.*; Albrecht-Schmitt, T. E.*; Choi, H. C.*; Zhu, J.-X.*; Thompson, J. D.*; et al.
Physical Review B, 99(3), p.035104_1 - 035104_6, 2019/01
被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)正方晶プルトニウムボロン化合物PuBの単結晶、および粉末試料を用いて、
Pu核核磁気共鳴(NMR)実験を行なった。この化合物は、最近になって強相関電子系のトポロジカル絶縁体候補物質と考えられている。
Pu核NMRスペクトルは、結晶内Pu位置の局所対称性を反映したものとなっており、NMRシフトとNMR緩和率の温度依存性は、エネルギーギャップをもつ非磁性状態にあることが示唆された。これは、密度汎関数理論計算結果とも矛盾しない。実際に観測された巨視的なギャップ状態は、本化合物がトポロジカル絶縁体候補であることを支持している。
Cheung, Y. W.*; Hu, Y. J.*; 今井 正樹*; 谷奥 泰明*; 金川 響*; 村川 譲一*; 森山 広大*; Zhang, W.*; Lai, K. T.*; 吉村 一良*; et al.
Physical Review B, 98(16), p.161103_1 - 161103_5, 2018/10
被引用回数:5 パーセンタイル:47.75(Materials Science, Multidisciplinary)Approaching a quantum critical point has been an effective route to stabilize superconductivity. While the role of magnetic QCPs has been extensively discussed, similar exploration of a structural QCP is scarce. Using inelastic X-ray scattering, we examine the phonon spectrum of the nonmagnetic quasi-skutterudite (CaSr
)
Rh
Sn
, which represents a precious system to explore the interplay between structural instabilities and superconductivity by tuning the Ca concentration x. We unambiguously detect the softening of phonon modes around the M point on cooling towards the structural transition. Intriguingly, at x = 0:85, the soft mode energy squared at the M point extrapolates to zero at -5.7 K, providing the first compelling microscopic evidence of a structural QCP in (Ca
Sr
)
Rh
Sn
. The enhanced phonon density-of-states at low energy provides the essential ingredient for realizing strong-coupling superconductivity near the structural QCP.
Xie, T.*; Wei, Y.*; Gong, D.*; Fennell, T.*; Stuhr, U.*; 梶本 亮一; 池内 和彦*; Li, S.*; Hu, J.*; Luo, H.*
Physical Review Letters, 120(26), p.267003_1 - 267003_7, 2018/06
被引用回数:14 パーセンタイル:15.87(Physics, Multidisciplinary)We report an inelastic neutron scattering study on the spin resonance in the bilayer iron-based superconductor CaKFeAs
. In contrast to its quasi-two-dimensional electron structure, three strongly
-dependent modes of spin resonance are found below
= 35 K. The mode energies are below and linearly scale with the total superconducting gaps summed on the nesting hole and electron pockets, essentially in agreement with the results in cuprate and heavy fermion superconductors. This observation supports the sign-reversed Cooper-pairing mechanism under multiple pairing channels and resolves the long-standing puzzles concerning the broadening and dispersive spin resonance peak in iron pnictides. More importantly, the triple resonant modes can be classified into odd and even symmetries with respect to the distance of Fe-Fe planes within the Fe-As bilayer unit. Thus, our results closely resemble those in the bilayer cuprates with nondegenerate spin excitations, suggesting that these two high-
superconducting families share a common nature.
Wang, C.*; Daiwei, Y.*; Liu, X.*; Chen, R.*; Du, X.*; Hu, B.*; Wang, L.*; 飯田 一樹*; 蒲沢 和也*; 脇本 秀一; et al.
Physical Review B, 96(8), p.085111_1 - 085111_5, 2017/08
被引用回数:3 パーセンタイル:71(Materials Science, Multidisciplinary)This paper presents a systematic study of spin and lattice dynamics in the quasi-one-dimensional spiral magnet CuBr, using Raman scattering in conjunction with infrared and neutron spectroscopy. Along with the development of spin correlations upon cooling, we observe a rich set of broad Raman bands at energies that correspond to phonon-dispersion energies near the one-dimensional magnetic wave vector. The low-energy bands further exhibit a distinct intensity maximum at the spiral magnetic ordering temperature.
酒井 宏典; Ronning, F.*; 服部 高典; 徳永 陽; 神戸 振作; Zhu, J.-X.*; Wakeham, N.*; 安岡 弘志; Bauer, E. D.*; Thompson, J. D.*
Journal of Physics; Conference Series, 807(3), p.032001_1 - 032001_6, 2017/04
被引用回数:0 パーセンタイル:100量子臨界金属CeCoInのInを少量のCdで置換した時の電子状態を核四重極共鳴(NQR)を用いて調べた。およそ半分のCd置換子周りで局所的にCeの局在モーメントが発生することを、縦緩和率
のサイト依存性から明らかにした。横緩和率
の測定も行い、局在スピン周りでは、
が温度
に比例し、一方、置換子から離れたところでは、
となっており、純CeCoIn
の
に近く、バルクの電子状態は量子臨界状態のままである。
Cheung, Y. W.*; Hu, Y. J.*; Goh, S. K.*; 金子 耕士; 筒井 智嗣; Logg, P. W.*; Grosche, F. M.*; 金川 響*; 谷奥 泰明*; 今井 正樹*; et al.
Journal of Physics; Conference Series, 807(3), p.032002_1 - 032002_4, 2017/04
被引用回数:3 パーセンタイル:14.89(CaSr
)
Rh
Sn
is a member of the substitution series (Ca
Sr
)
Rh
Sn
which has recently been argued to feature a structural quantum critical point at
= 0.9. In the stoichiometric compound Sr
Rh
Sn
, the structural transition at
138 K has been shown to be a second-order phase transition. Moving towards xc, we examine the character of the structural transition in (Ca
Sr
)
Rh
Sn
(i.e.
= 0.5,
55 K) using electrical resistivity, heat capacity and X-ray scattering. The absence of the thermal hysteresis in specific heat around
, and the continuous evolution of the superlattice reflection detected by X-ray diffraction are consistent with the scenario that the structural transition associated with a modulation vector
= (0.5, 0.5, 0) in (Ca
Sr
)
Rh
Sn
remains second-order on approaching the quantum critical point.
Barzakh, A.*; Andreyev, A.; Cocolios, T. E.*; de Groote, R. P.*; Fedorov, D. V.*; Fedosseev, V. N.*; Ferrer, R.*; Fink, D. A.*; Ghys, L.*; Huyse, M.*; et al.
Physical Review C, 95(1), p.014324_1 - 014324_12, 2017/01
被引用回数:14 パーセンタイル:11.71(Physics, Nuclear)Hyperfine structure and isotope shifts have been measured for the ground and isomeric states in the neutron deficient isotopes Tl using the 276.9 nm transition. The experiment has been performed at the CERN Isotope Separator On-Line facility using the in-source resonance-ionization laser spectroscopy technique. Spins for the ground states in
Tl have been determined as
= 1/2. Magnetic moments and changes in the nuclear mean-square charge radii have been deduced. By applying the additivity relation for magnetic moments of the odd-odd Tl nuclei the leading configuration assignments were confirmed. A deviation of magnetic moments for isomeric states in
Tl from the trend of the heavier Tl nuclei is observed. The charge radii of the ground states of the isotopes
Tl follow the trend for isotonic (spherical) lead nuclei. The noticeable difference in charge radii for ground and isomeric states of
Tl has been observed, suggesting a larger deformation for the intruder-based 9/2
and 10
states compared to the ground states. An unexpected growth of the isomer shift for
Tl has been found.
Lopez-Martens, A.*; Henning, G.*; Khoo, T. L.*; Seweryniak, D.*; Alcorta, M.*; 浅井 雅人; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.
EPJ Web of Conferences, 131, p.03001_1 - 03001_6, 2016/12
被引用回数:1 パーセンタイル:48.2原子番号が100を超える原子核の核分裂障壁の高さとその角運動量依存性を初めて測定した。核分裂による崩壊が優勢となり始める励起エネルギーを決定できる初期分布法という方法をNoの測定に適用した。
Noの核分裂障壁はスピンゼロにおいて6.6MeVと決定された。このことは、
Noが原子核の殻効果によって強く安定化されていることを示している。
Truesdale, V. L.*; Andreyev, A.; Ghys, L.*; Huyse, M.*; Van Duppen, P.*; Sels, S.*; Andel, B.*; Antalic, S.*; Barzakh, A.*; Capponi, L.*; et al.
Physical Review C, 94(3), p.034308_1 - 034308_11, 2016/09
被引用回数:7 パーセンタイル:37.47(Physics, Nuclear)A nuclear-decay spectroscopy study of the neutron-deficient isotope At is reported where an isotopically pure beam was produced using the selective Resonance Ionization Laser Ion Source and On-Line Isotope Mass Separator (CERN). The fine-structure
decay of
At allowed the low-energy excited states in the daughter nucleus
Bi to be investigated. A
-delayed fission study of
At was also performed. A mixture of symmetric and asymmetric fission-fragment mass distributions of the daughter isotope
Po (populated by
decay of
At) was deduced based on the measured fission-fragment energies. A
DF probability
(
At) = 9(1)
10
was determined.
Hota, S.*; Tandel, S.*; Chowdhury, P.*; Ahmad, I.*; Carpenter, M. P.*; Chiara, C. J.*; Greene, J. P.*; Hoffman, C. R.*; Jackson, E. G.*; Janssens, R. V. F.*; et al.
Physical Review C, 94(2), p.021303_1 - 021303_5, 2016/08
被引用回数:5 パーセンタイル:48.22(Physics, Nuclear)Puにおける
= 8
アイソマーからの崩壊と集団的バンド構造が
Tiと
Pbのビームによる深部非弾性散乱実験によって調べられた。バンド内の正確な
分岐比の測定によって、偶
,
=150アイソトーンにおける
= 8
二準中性子アイソマーが9/2
[734]
7/2
[624]
の配位であることを確かめた。
=152における変形シェルギャップ近傍のこれらのアイソマーは、超重核の一粒子エネルギーの理論的な予言において重要なベンチマークとなる。
Cheung, Y. W.*; Zhang, J. Z.*; Zhu, J. Y.*; Yu, W. C.*; Hu, Y. J.*; Wang, D. G.*; 大友 優香*; 岩佐 和晃*; 金子 耕士; 今井 正樹*; et al.
Physical Review B, 93(24), p.241112_1 - 241112_5, 2016/06
被引用回数:12 パーセンタイル:34.19(Materials Science, Multidisciplinary)The quasi-skutterudite superconductor LaCo
Sn
undergoes a phase transition at
= 152 K. By measuring the temperature dependence of heat capacity, electrical resistivity, and the superlattice reflection intensity using X-ray, we explore the character of the phase transition at
. Our lattice dynamic calculations found imaginary phonon frequencies around the
point, when the high temperature structure is used in the calculations, indicating that the structure is unstable at the zero temperature limit. The combined experimental and computational results establish that
is associated with a second-order structural transition with
= (0.5, 0.5, 0) (or the
point). Further electronic band structure calculations reveal Fermi surface sheets with low-curvature segments, which allow us to draw qualitative comparison with both Sr
Ir
Sn
and Sr
Rh
Sn
in which similar physics has been discussed recently.
Van Beveren, C.*; Andreyev, A.; Barzakh, A. E.*; Cocolios, T. E.*; de Groote, R. P.*; Fedorov, D.*; Fedosseev, V. N.*; Ferrer, R.*; Ghys, L.*; Huyse, M.*; et al.
Journal of Physics G; Nuclear and Particle Physics, 43(2), p.025102_1 - 025102_22, 2016/02
被引用回数:8 パーセンタイル:33.58(Physics, Nuclear)-decay spectroscopy of
Tl has been performed at the CERN isotope separator on-line (ISOLDE) facility. New fine-structure
decays have been observed for both isotopes.
-decay branching ratios of 0.089(19)
, 0.047(6)
and 1.22(30)
have been deduced for the (10
), (7
) and (2
) states respectively in
Tl and a lower limit of 0.49
for the
-decay branching ratio of
Tl. A new half-life of 9.5(2) s for the (2
) state in
Tl and 1.9(1) s for the low-spin state in
Tl has been deduced. Using
-
coincidence analysis, multiple
rays were observed de-exciting levels in
Au fed by
Tl
decays. The
transitions connecting these low-lying states in
Au are essential to sort the data and possibly identify bands from inbeam studies in these isotopes. Owing to the complex fine-structure
decays and limited knowledge about the structure of the daughter nuclei, only partial level schemes could be constructed for both gold isotopes in the present work. Reduced
-decay widths have been calculated and are compared with values obtained in neighboring odd-A and even-A thallium isotopes. Except for the allowed
decay of the
Tl (10
) state, the other fine-structure
decays observed in this study are hindered. This points to strong structural changes between parent thallium and daughter gold isotopes.
Ye, M.*; Li, W.*; Zhu, S.-Y.*; 竹田 幸治; 斎藤 祐児; Wang, J.*; Pan, H.*; Nurmamat, M.*; 角田 一樹*; Ji, F.*; et al.
Nature Communications (Internet), 6, p.8913_1 - 8913_7, 2015/11
被引用回数:35 パーセンタイル:9.98(Multidisciplinary Sciences)磁性元素を添加したトポロジカル絶縁体は、量子異常ホール効果や無散逸伝導などの魅力的な現象の発現が予言され、低消費電力スピンデバイスの開発につながっていくものと期待されている。既に、いくつかの磁性添加トポロジカル絶縁体で長距離磁気秩序が確認されている。しかし、量子異常ホール効果の発現は、極低温におけるCrを添加した(Sb,Bi)Te
系に限られており、強磁性の微視的な起源はほとんど分かっていない。そこで、今回、X線磁気円二色性実験による元素選択的研究を行うことにより、本物質系の強磁性は、母体の正孔キャリアーを媒介としたものであり、Crの3d電子とSbやTeのp電子の相互作用が極めて重要であることを明らかにした。この結果は、異常量子ホール素子の実現に向けても重要である。
酒井 宏典; Ronning, F.*; Zhu, J.-X.*; Wakeham, N.*; 安岡 弘志; 徳永 陽; 神戸 振作; Bauer, E. D.*; Thompson, J. D.*
Physical Review B, 92(12), p.121105_1 - 121105_5, 2015/09
被引用回数:13 パーセンタイル:37.77(Materials Science, Multidisciplinary)核四重極共鳴(NQR)法を用いて、SnやCdを置換した量子臨界金属CeCoInについて微視的研究を行った。その結果、両置換子によって誘起される局所的電子状態は、かなり異なっていることが分かった。この知見は、一般的に置換系で見られる系毎に異なる非フェルミ液体的挙動を統一的に説明することに役立つかも知れない。
Van Beveren, C.*; Andreyev, A.; Barzakh, A.*; Cocolios, T. E.*; Fedorov, D.*; Fedosseev, V. N.*; Ferrer, R.*; Huyse, M.*; Kster, U.*; Lane, J. F. W.*; et al.
Physical Review C, 92(1), p.014325_1 - 014325_8, 2015/07
被引用回数:7 パーセンタイル:42.31(Physics, Nuclear)Decay spectroscopy of Tl has been performed at the CERN Isotope Separator On-Line (ISOLDE) facility. An excitation energy of 506.1(1) keV and a half-life of 47.1(7) ms of the intruder based (10
) state have been extracted. The internal decay characteristics of this state are determined and discussed, extending the systematics of such states in the even-mass thallium nuclei below neutron midshell at N = 104. The retardation factors of the isomeric M2 and E3 transitions are deduced and compared with retardation factors in neighboring odd-mass and even-mass thallium isotopes. The new information is combined with a review of hindered and unhindered
-decay data of
Bi populating levels in daughter nuclei
Tl and supports the interpretation of the intruder character of the (10
) state in
Tl.
角田 一樹*; 白井 開渡*; Zhu, S.-Y.*; 谷口 雅樹*; Ye, M.*; 上田 茂典*; 竹田 幸治; 斎藤 祐児; Aseguinolaza, I. R.*; Barandiarn, J. M.*; et al.
Physical Review B, 91(13), p.134417_1 - 134417_6, 2015/04
被引用回数:4 パーセンタイル:73.73(Materials Science, Multidisciplinary)The temperature evolution of the electronic structure of a Ni-Fe(Co)-Ga/MgO(100), Heusler-type, ferromagnetic shape-memory alloy thin film has been followed by a bulk-sensitive hard X-ray photoelectron spectroscopy, element-selective soft X-ray magnetic circular dichroism, and first-principles calculation. The reversible changes of the electronic states near the Fermi energy show a hysteresis associated with the martensitic phase transition (MPT), where the pseudogap opens on cooling and closes again on warming. In addition, the Ni 3d spin magnetic moment increases by approximately two times across the MPT, whereas the change of Fe 3d moment is moderate. By comparing the experimental results with the calculated spin-resolved density of states, we conclude that the band Jahn-Teller effect of Ni 3d and Fe 3d orbitals is responsible for MPT.
Chiara, C. J.*; Weisshaar, D.*; Janssens, R. V. F.*; 角田 佑介*; 大塚 孝治*; Harker, J. L.*; Walters, W. B.*; Recchia, F.*; Albers, M.*; Alcorta, M.*; et al.
Physical Review C, 91(4), p.044309_1 - 044309_10, 2015/04
被引用回数:25 パーセンタイル:9.31(Physics, Nuclear)アルゴンヌ国立研究所にて中性子過剰核Niを
Znの多核子移行反応によって生成し、
線検出器GRETINAを用いて
線分光を行った。その結果、
,
準位を初めて観測した。これらの準位は小さな模型空間を採用した殻模型計算では再現されないため、陽子の
軌道からの励起を伴った大きな変形状態であると考えられる。本論文の理論グループが2014年に発表した大規模殻模型計算によって
Niの励起状態を解析した結果、これらの状態は大きなプロレート変形を持つ状態とよく対応することがわかった。この結果は、中性子過剰ニッケル同位体における変形共存が
Ni以外にも存在することを実証するとともに、中性子過剰核における大規模殻模型計算の予言能力を確かめるものである。