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論文

Topological characterization of classical waves; The Topological origin of magnetostatic surface spin waves

山本 慧; Thiang, G. C.*; Pirro, P.*; Kim, K.-W.*; Everschor-Sitte, K.*; 齊藤 英治*

Physical Review Letters, 122(21), p.217201_1 - 217201_5, 2019/05

https://doi.org/10.1103/PhysRevLett.122.217201

We propose a topological characterization of Hamiltonians describing classical waves. Applying it to the magnetostatic surface spin waves that are important in spintronics applications, we settle the speculation over their topological origin. For a class of classical systems that includes spin waves driven by dipole-dipole interactions, we show that the topology is characterized by vortex lines in the Brillouin zone in such a way that the symplectic structure of Hamiltonian mechanics plays an essential role. We define winding numbers around these vortex lines and identify them to be the bulk topological invariants for a class of semimetals. Exploiting the bulk-edge correspondence appropriately reformulated for these classical waves, we predict that surface modes appear but not in a gap of the bulk frequency spectrum. This feature, consistent with the magnetostatic surface spin waves, indicates a broader realm of topological phases of matter beyond spectrally gapped ones.

論文

Coexistence of ferromagnetic and stripe-type antiferromagnetic spin fluctuations in YFe$$_{2}$$Ge$$_{2}$$

Wo, H.*; Wang, Q.*; Shen, Y.*; Zhang, X.*; Hao, Y.*; Feng, Y.*; Shen, S.*; He, Z.*; Pan, B.*; Wang, W.*; et al.

Physical Review Letters, 122(21), p.217003_1 - 217003_5, 2019/05

https://doi.org/10.1103/PhysRevLett.122.217003

We report neutron scattering measurements of single-crystalline YFe$$_{2}$$Ge$$_{2}$$ in the normal state, which has the same crystal structure as the 122 family of iron pnictide superconductors. YFe$$_{2}$$Ge$$_{2}$$ does not exhibit long-range magnetic order but exhibits strong spin fluctuations. Like the iron pnictides, YFe$$_{2}$$Ge$$_{2}$$ displays anisotropic stripe-type antiferromagnetic spin fluctuations at ($$pi$$, 0, $$pi$$). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wave vector (0, 0, $$pi$$). These ferromagnetic spin fluctuations are isotropic in the ($$H$$, $$K$$) plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in YFe$$_{2}$$Ge$$_{2}$$ and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.

論文

Strong correlation between ferromagnetic superconductivity and pressure-enhanced ferromagnetic fluctuations in UGe$$_2$$

立岩 尚之; 芳賀 芳範; 山本 悦嗣

Physical Review Letters, 121(23), p.237001_1 - 237001_6, 2018/12

http://dx.doi.org/10.1103/PhysRevLett.121.237001
 被引用回数：1 パーセンタイル：49.95(Physics, Multidisciplinary)

ウラン系強磁性超伝導物質UGe$$_2$$の高圧下磁化測定を行い、データをTakahashiによるスピンのゆらぎ理論を用いて解析した。強磁性相FM1とFM2の相境界$$P_x$$で、スピンゆらぎスペクトルの分布幅$$T_0$$に明確な異常が現れた。$$P_x$$では、超伝導転移温度$$T_{rm sc}$$が最大値を示す。このことは、$$P_x$$近辺で発達する強磁性スピンのゆらぎが超伝導出現に役割を果たすことを示唆する。また、パラメーター$${T_{rm Curie}}/{T_0}$$(ここで、$${T_{rm Curie}}$$は強磁性転移温度)の圧力変化から、局在性の強いFM2から遍歴性の強いFM1へ基底状態は転移することが示唆された。$$T_0$$と$$T_{rm sc}$$の関係について、銅酸化物超伝導体等、他の超伝導物質と議論された。

論文

First evidence for cos 2$$beta >$$ 0 and resolution of the Cabibbo-Kobayashi-Maskawa Quark-Mixing Unitarity Triangle ambiguity

足立 一郎*; 谷田 聖; Belle Collaboration*; 他421名*

Physical Review Letters, 121(26), p.261801_1 - 261801_11, 2018/12

http://dx.doi.org/10.1103/PhysRevLett.121.261801
 被引用回数：1 パーセンタイル：49.95(Physics, Multidisciplinary)

We present first evidence that the cosine of the $$CP$$-violating weak phase $$2beta$$ is positive, and hence exclude trigonometric multifold solutions of the CKM Unitarity Triangle using a time-dependent Dalitz plot analysis of $$B^{0} to D^{(*)} h^{0}$$ with $$D to K_{S}^{0} pi^{+} pi^{-}$$ decays, where $$h^{0} in {pi^{0}, eta, omega }$$ denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BaBar and Belle experiments collected at the $$Upsilon(4S)$$ resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain $$( 471 pm 3 )times 10^6, Bbar{B}$$ pairs recorded by the BaBar detector and $$( 772 pm 11 )times 10^6, Bbar{B}$$ pairs recorded by the Belle detector. The results of the measurement are $$sin{2beta} = 0.80 pm 0.14 ,(rm{stat.}) pm 0.06 ,(rm{syst.}) pm 0.03 ,(rm{model})$$ and $$cos{2beta} = 0.91 pm 0.22 ,(rm{stat.}) pm 0.09 ,(rm{syst.}) pm 0.07 ,(rm{model})$$. The result for the direct measurement of the angle $$beta$$ of the CKM Unitarity Triangle is $$beta = left( 22.5 pm 4.4 ,(rm{stat.}) pm 1.2 ,(rm{syst.}) pm 0.6 ,(rm{model}) right)^{circ}$$. The quoted model uncertainties are due to the composition of the $$D^{0} to K_{S}^{0} pi^{+} pi^{-}$$ decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics $$e^{+}e^{-} to cbar{c}$$ data sample. CP violation is observed in $$B^{0} to D^{(*)} h^{0}$$ decays at the level of $$5.1$$ standard deviations. The significance for $$cos{2beta} > 0$$ is $$3.7$$ standard deviations. The trigonometric multifold solution $$pi/2 - beta = (68.1 pm 0.7)^{circ}$$ is excluded at the level of $$7.3$$ standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.

論文

Observation of $$Upsilon(2S)togamma eta_{b}(1S)$$ decay

Fulsom, B. G.*; 谷田 聖; Belle Collaboration*; 他197名*

Physical Review Letters, 121(23), p.232001_1 - 232001_8, 2018/12

http://dx.doi.org/10.1103/PhysRevLett.121.232001
 パーセンタイル：100(Physics, Multidisciplinary)

We report the observation of $$Upsilon(2S)togammaeta_{b}(1S)$$ decay based on analysis of the inclusive photon spectrum of $$24.7$$ fb$$^{-1}$$ of $$e^+ e^-$$ collisions at the $$Upsilon(2S)$$ center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy $$e^+ e^-$$ collider. We measure a branching fraction of $$mathcal{B}(Upsilon(2S)togammaeta_{b}(1S))=(6.1^{+0.6+0.9}_{-0.7-0.5})times 10^{-4}$$, and derive an $$eta_{b}(1S)$$ mass of $$9394.8^{+2.7+4.5}_{-3.1-2.7}$$ MeV/$$c^{2}$$, where the uncertainties are statistical and systematic, respectively. The significance of our measurement is greater than 7 standard deviations, constituting the first observation of this decay mode.

論文

Pseudorapidity dependence of particle production and elliptic flow in asymmetric nuclear collisions of $$p$$+Al, $$p$$+Au, $$d$$+Au, and $$^{3}$$He+Au at $$sqrt{s_{_{NN}}}$$ = 200 GeV

Adare, A.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他362名*

Physical Review Letters, 121(22), p.222301_1 - 222301_8, 2018/11

http://dx.doi.org/10.1103/PhysRevLett.121.222301
 被引用回数：3 パーセンタイル：29.91(Physics, Multidisciplinary)

Asymmetric nuclear collisions of $$p$$+Al, $$p$$+Au, $$d$$+Au, and $$^{3}$$He+Au at $$sqrt{s_{_{NN}}}$$ = 200 GeV provide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production $$dN_{rm ch}/deta$$ in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow $$v_{2}$$ over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.

論文

Observation of an excited $$Omega^-$$ Baryon

Yelton, J.*; 谷田 聖; Belle Collaboration*; 他190名*

Physical Review Letters, 121(5), p.052003_1 - 052003_7, 2018/08

http://dx.doi.org/10.1103/PhysRevLett.121.052003
 被引用回数：7 パーセンタイル：6.69(Physics, Multidisciplinary)

Using data recorded with the Belle detector, we observe a new excited hyperon, an $$Omega^{*-}$$ candidate decaying into $$Xi^0K^-$$ and $$Xi^-K^0_S$$ with a mass of $$2012.4pm0.7 {rm (stat)pm 0.6 (rm syst)} {rm MeV}/c^2$$ and a width of $$Gamma=6.4^{+2.5}_{-2.0} {rm(stat)}pm1.6 {rm(syst)} {rm MeV}$$. The $$Omega^{*-}$$ is seen primarily in $$Upsilon(1S), Upsilon(2S)$$, and $$Upsilon(3S)$$ decays.

論文

Observation of $$Upsilon(4S)to eta' Upsilon(1S)$$

Guido, E.*; 谷田 聖; Belle Collaboration*; 他168名*

Physical Review Letters, 121(6), p.062001_1 - 062001_7, 2018/08

http://dx.doi.org/10.1103/PhysRevLett.121.062001
 パーセンタイル：100(Physics, Multidisciplinary)

We report the first observation of the hadronic transition $$Upsilon(4S)toeta'Upsilon(1S)$$, using 496 fb$$^{-1}$$ data collected at the $$Upsilon(4S)$$ resonance with the Belle detector at the KEKB asymmetric-energy $$e^{+}e^{-}$$ collider. We reconstruct the $$eta'$$ meson through its decays to $$rho^0gamma$$ and to $$pi^+pi^-eta$$, with $$etatogammagamma$$. We measure: $${cal B}(Upsilon(4S)toeta'Upsilon(1S))=(3.43pm 0.88 {rm(stat.)} pm 0.21 {rm(syst.)})times10^{-5}$$, with a significance of 5.7$$sigma$$.

論文

Search for $$B^{-}tomu^{-}barnu_mu$$ decays at the Belle experiment

Sibidanov, A.*; 谷田 聖; Belle Collaboration*; 他187名*

Physical Review Letters, 121(3), p.031801_1 - 031801_8, 2018/07

http://dx.doi.org/10.1103/PhysRevLett.121.031801
 被引用回数：3 パーセンタイル：20.01(Physics, Multidisciplinary)

We report the result of a search for the decay $$B^{-}tomu^{-}barnu_mu$$. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic $$B$$-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of $${cal B}(B^{-}tomu^{-}barnu_mu) =(6.46 pm 2.22 pm 1.60) times10^{-7}$$ or a frequentist 90% confidence level interval on the $$B^{-}tomu^{-}barnu_mu$$ branching fraction of $$[2.9, 10.7]times 10^{-7}$$. This result is obtained from a 711 fb$$^{-1}$$ data sample that contains $$772 times 10^6$$ $$Bbar{B}$$ pairs, collected near the $$Upsilon(4S)$$ resonance with the Belle detector at the KEKB asymmetric-energy $$e^+ e^-$$ collider.

論文

$$^7$$Be(n,p)$$^7$$Li reaction and the cosmological lithium problem; Measurement of the cross section in a wide energy range at n_TOF at CERN

Damone, L.*; Barbagallo, M.*; Mastromarco, M.*; Cosentino, L.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他152名*

Physical Review Letters, 121(4), p.042701_1 - 042701_7, 2018/07

https://doi.org/10.1103/PhysRevLett.121.042701

We report on the measurement of the $$^7$$Be(n,p)$$^7$$Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a $$^7$$Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal $$^7$$Li(p,n)$$^7$$Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near threshold neutron production in the p+$$^7$$Li reaction is also discussed.

論文

Odd and even modes of neutron spin resonance in the bilayer iron-based superconductor CaKFe$$_{4}$$As$$_{4}$$

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

http://dx.doi.org/10.1103/PhysRevLett.120.267003
 被引用回数：3 パーセンタイル：20.01(Physics, Multidisciplinary)

We report an inelastic neutron scattering study on the spin resonance in the bilayer iron-based superconductor CaKFe$$_4$$As$$_4$$. In contrast to its quasi-two-dimensional electron structure, three strongly $$L$$-dependent modes of spin resonance are found below $$T_c$$ = 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-$$T_c$$ superconducting families share a common nature.

論文

Quantitative characterization of the nanoscale local lattice strain induced by Sr dopants in La$$_{1.92}$$Sr$$_{0.08}$$CuO$$_{4}$$

Lin, J. Q.*; Liu, X.*; Blackburn, E.*; 脇本 秀一; Ding, H.*; Islam, Z.*; Sinha, S. K.*

Physical Review Letters, 120(19), p.197001_1 - 197001_6, 2018/05

http://dx.doi.org/10.1103/PhysRevLett.120.197001
 パーセンタイル：100(Physics, Multidisciplinary)

X線散漫散乱の観測により、銅酸化物高温超伝導体La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$中の不純物Srにより生じるナノスケールの格子歪みを観測した。この結果は、これまで議論となっていた不純物による歪みの性質を明らかにしたとともに、STMで観測されているギャップの不均一性の原因ではないことを明らかにした。

論文

First direct mass measurements of nuclides around $$Z$$ = 100 with a multireflection time-of-flight mass spectrograph

伊藤 由太*; Schury, P.*; 和田 道治*; 新井 郁也*; 羽場 宏光*; 平山 賀一*; 石澤 倫*; 加治 大哉*; 木村 創大*; 小浦 寛之; et al.

Physical Review Letters, 120(15), p.152501_1 - 152501_6, 2018/04

http://dx.doi.org/10.1103/PhysRevLett.120.152501
 被引用回数：11 パーセンタイル：3.78(Physics, Multidisciplinary)

冷たい核融合反応および熱い融合反応によって生成した変形閉殻中性子数152の近傍に位置する原子核$$^{246}$$Es, $$^{251}$$Fm、および超フェルミウム原子核$$^{249-252}$$Md, $$^{254}$$Noの質量の直接測定を、多反射時間飛行質量分析装置(MR-TOF)を用いて実施した。$$^{246}$$Esおよび$$^{249,250,252}$$Mdの質量測定は世界で初めての成果である。さらに$$^{249,250}$$Mdの質量を$$alpha$$崩壊連鎖のアンカーポイントとして用いて$$^{261}$$Bhおよび$$^{266}$$Mtまでの重い原子核の質量を決定した。これらの新測定された質量を理論質量計算と比較し、巨視的・微視的模型の予測値と良い一致が見られることを示した。近接する3つの質量値から求められる経験的殻ギャップエネルギー$$delta_{2n}$$を今回の質量値から求め、MdおよびLrに対する変形閉殻中性子数$$N=152$$の存在を裏付ける結果を得た。

論文

First determination of the level structure of an $$sd$$-shell hypernucleus, $$^{19}_{Lambda}$$F

Yang, S. B.*; 江川 弘行; 長谷川 勝一; 早川 修平; 細見 健二; 市川 裕大; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; et al.

Physical Review Letters, 120, p.132505_1 - 132505_5, 2018/03

http://dx.doi.org/10.1103/PhysRevLett.120.132505
 被引用回数：1 パーセンタイル：49.95(Physics, Multidisciplinary)

We report on the first observation of $$gamma$$ rays emitted from an $$sd$$-shell hypernucleus, $$^{19}_{Lambda}$$F. The energy spacing between the ground state doublet, $$1/2^+$$ and $$3/2^+$$ states, of $$^{19}_{Lambda}$$F is determined to be $$315.5pm0.4({rm stat.})^{+0.6}_{-0.5}({rm syst.})$$ keV by measuring the $$gamma$$-ray energy of the $$M1(3/2^+ to 1/2^+)$$ transition. In addition, three $$gamma$$-ray peaks are observed and assigned as $$E2(5/2^+ to 1/2^+)$$, $$E1(1/2^- to 1/2^+)$$, and $$E1(1/2^- to 3/2^+)$$ transitions. The excitation energies of the $$5/2^+$$ and $$1/2^-$$ states are determined to be $$895.2pm0.3({rm stat.})pm0.5({rm syst.})$$ keV and $$1265.6pm1.2({rm stat.})^{+0.5}_{-0.7}({rm syst.})$$ keV, respectively. It is found that the ground state doublet spacing is well described by theoretical models based on existing $$s$$- and $$p$$-shell hypernuclear data.

論文

Experimental determination of the topological phase diagram in Cerium monopnictides

黒田 健太*; 越智 正之*; 鈴木 博之*; 平山 元昭*; 中山 光大*; 野口 亮*; Bareille, C.*; 明比 俊太朗*; 國定 聡*; 室 隆桂之*; et al.

Physical Review Letters, 120(8), p.086402_1 - 086402_6, 2018/02

http://dx.doi.org/10.1103/PhysRevLett.120.086402
 被引用回数：6 パーセンタイル：10.74(Physics, Multidisciplinary)

We use bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy and investigate bulk electronic structures of Ce monopnictides (CeX; X=P, As, Sb and Bi). By exploiting a paradigmatic study of the band structures as a function of their spin-orbit coupling (SOC), we draw the topological phase diagram of CeX and unambiguously reveal the topological phase transition from a trivial to a nontrivial regime in going from CeP to CeBi induced by the band inversion.

論文

Measurements of multiparticle correlations in $$d$$+Au Collisions at 200, 62.4, 39, and 19.6 GeV and $$p$$+Au Collisions at 200 GeV and implications for collective behavior

Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他311名*

Physical Review Letters, 120(6), p.062302_1 - 062302_8, 2018/02

http://dx.doi.org/10.1103/PhysRevLett.120.062302
 被引用回数：8 パーセンタイル：5.39(Physics, Multidisciplinary)

Recently, multiparticle-correlation measurements of relativistic $$p/d/^3$$He$$+$$Au, $$p$$$$+$$Pb, and even $$p$$$$+$$$$p$$ collisions have shown surprising collective signatures. Here we present beam-energy-scan measurements of 2-, 4-, and 6-particle angular correlations in $$d$$$$+$$Au collisions at $$sqrt{s_{_{NN}}}$$=200, 62.4, 39, and 19.6 GeV. We also present measurements of 2- and 4-particle angular correlations in $$p$$$$+$$Au collisions at $$sqrt{s_{_{NN}}}$$=200 GeV. We find the 4-particle cumulant to be real-valued for $$d$$$$+$$Au collisions at all four energies. We also find that the 4-particle cumulant in $$p$$$$+$$Au has the opposite sign as that in $$d$$$$+$$Au, indicating that the correlations are geometrical and therefore collective in origin. Further we find that the 6-particle cumulant agrees with the 4-particle cumulant in $$d$$$$+$$Au collisions at 200 GeV, which indicates that nonflow effects are subdominant and provides strong evidence of collectivity.

論文

Nuclear dependence of the transverse-single-spin asymmetry for forward neutron production in polarized $$p$$$$+$$$$A$$ collisions at $$sqrt{s_{_{NN}}}=200$$ GeV

Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他309名*

Physical Review Letters, 120, p.022001_1 - 022001_9, 2018/01

http://dx.doi.org/10.1103/PhysRevLett.120.022001
 被引用回数：2 パーセンタイル：29.91(Physics, Multidisciplinary)

During 2015 the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized $$p+p$$ collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in $$p+p$$ collisions predicts only a moderate atomic-mass-number ($$A$$) dependence. In contrast, the asymmetries observed at RHIC in $$p+A$$ collisions showed a surprisingly strong $$A$$ dependence in inclusive forward neutron production. The observed asymmetry in $$p$$+Al collisions is much smaller, while the asymmetry in $$p$$ + Au collisions is a factor of three larger in absolute value and of opposite sign. The interplay of different neutron production mechanisms is discussed as a possible explanation of the observed $$A$$ dependence.

論文

Evidence for spin singlet pairing with strong uniaxial anisotropy in URu$$_2$$Si$$_2$$ using nuclear magnetic resonance

服部 泰佑; 酒井 宏典; 徳永 陽; 神戸 振作; 松田 達磨*; 芳賀 芳範

Physical Review Letters, 120(2), p.027001_1 - 027001_5, 2018/01

http://dx.doi.org/10.1103/PhysRevLett.120.027001
 被引用回数：3 パーセンタイル：29.91(Physics, Multidisciplinary)

In order to identify the spin contribution to superconducting pairing compatible with the so-called "hidden order", $$^{29}$$Si nuclear magnetic resonance measurements have been performed using a high-quality single crystal of URu$$_2$$Si$$_2$$. A clear reduction of the $$^{29}$$Si Knight shift in the superconducting state has been observed under magnetic field applied along the crystalline $$c$$ axis, corresponding to the magnetic easy axis. These results provide direct evidence for the formation of spin-singlet Cooper pairs. Consequently, results indicating a very tiny change of in-plane Knight shift reported previously demonstrate extreme uniaxial anisotropy for the spin susceptibility in the hidden order state.

論文

Spin current noise of the spin Seebeck effect and spin pumping

松尾 衛*; 大沼 悠一; 加藤 岳生*; 前川 禎通

Physical Review Letters, 120(3), p.037201_1 - 037201_5, 2018/01

http://dx.doi.org/10.1103/PhysRevLett.120.037201
 被引用回数：6 パーセンタイル：10.74(Physics, Multidisciplinary)

常磁性金属と強磁性体の二層系におけるスピンゼーベック効果及びスピンポンピングによって生成された純スピン流の揺らぎを理論的に調べた。スピンの保存と非保存の過程を考慮した強磁性体/金属の単純な界面のモデルから出発し、強磁性体/金属の結合強度について2次の摂動の範囲で、界面におけるスピン流とスピン流ノイズの一般的な式を導出した。また、イットリウム鉄ガーネットと白金の二層系を想定し、スピン流とスピン流ノイズを見積もった。その結果、界面におけるスピン非保存過程によって変調された、マグノンが運ぶ有効スピンを、スピン流ノイズを用いて決定できることを示した。加えて、スピン流ノイズによって、マグノンの有効スピン、スピンポンピングにおいて発生する界面での発熱量、常磁性金属のスピンホール角に関する情報が得られることを示した。

論文

Role of multichance fission in the description of fission-fragment mass distributions at high energies

廣瀬 健太郎; 西尾 勝久; 田中 翔也*; L$'e$guillon, R.*; 牧井 宏之; 西中 一朗*; Orlandi, R.; 塚田 和明; Smallcombe, J.*; Vermeulen, M. J.; et al.

Physical Review Letters, 119(22), p.222501_1 - 222501_6, 2017/12

http://dx.doi.org/10.1103/PhysRevLett.119.222501
 被引用回数：12 パーセンタイル：11.2(Physics, Multidisciplinary)

JAEAタンデム加速器施設で行った$$^{18}$$O+$$^{238}$$U反応における多核子移行チャンネルを用いた実験により、$$^{237-240}$$U, $$^{239-242}$$Np、および$$^{241-244}$$Puの核分裂質量分布を励起エネルギー10$$sim$$60MeVにおいて測定した。これらのうち、$$^{240}$$U, $$^{240,241,242}$$Npのデータは本実験により初めて観測された。原子核の殻効果の減衰によって対称分裂すると予想されていた高励起エネルギーにおいても、質量分布が非対称を示すことがわかった。搖動散逸定理に基づく動力学モデル計算との比較から、この振る舞いはマルチチャンス核分裂によるものであることを明らかにした。

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