平成２４年度 組織的な若手研究者等海外派遣プログラム 帰国報告書 （サマー／ウィンタースクール・インターンシップ・研究留学） 提出日：平成 24 年 12 月 27 日 フリガナ 氏 名 クレ 呉 マミコ 麻美子 所属 大学院 人間文化創成科学研究科 博士前期課程 理学専攻 物理科学コース 1 年 派遣先名 Institut Laue-Lan ge vin ラ ウ エ ラ ン ジ ュ バ ン 研 究 所 （ フ ラ ン ス ） （国名） Helmholtz-Zentrum B erlin ヘ ル ム ホ ル ツ セ ン タ ー ベ ル リ ン 研 究 所 （ ド イ ツ ） （日本出発日） 派遣期間 研究 テーマ 指導教員 氏名 ～ （日本到着日） 平成 24 年 12 月 2 日 ～ 平成 24 年 12 月 14 日 (研究留学の場合のみ) 中性子小角散乱実験による BaFe2(As,P)2 , LaNiC2, Sr2RuO4 の磁束格子の観測 古川はづき ㊞ ① 私は本プログラムによって、12 月前半の 2 週間、フランスのラ ウ エ ラ ン ジ ュ バ ン 研 究 所 、お よ びドイツのヘルムホルツセンターベルリン研究所の 2 か所での中性子小角散乱実験に参 加する機会を得ました。中性子散乱実験に参加したことがなかった私にとって、今回の 研究留学によって 1 度に 2 か所での実験を経験できたことは非常に貴重で幸運な体験で し た 。 12 月 2 日 に 日 本 を 出 国 し 、 フ ラ ン ス の リ ヨ ン 空 港 に 到 着 し ま し た 。 リ ヨ ン 空 港 か ら ラ ウ エ ラ ン ジ ュ バ ン 研 究 所 近 く ま で は バ ス で 移 動 し 、2 日 夜 遅 く に 研 究 所 に 到 着 し ま し た。3 日朝から実験を開始し、7 日の朝にフランスでの実験は終了しました。滞在中は研 究所の敷地内にあるゲストハウスに宿泊しました。実験は時に深夜や明け方まで続くこ と も あ り 、寝 不 足 に な る 日 も あ り ま し た が 、そ の 甲 斐 あ っ て BaFe2(As,P)2 と LaNiC2 の測定デー タを得ることができました。 7 日 に フ ラ ン ス か ら ド イ ツ の ベ ル リ ン に 移 動 す る 予 定 で し た が 、雪 に よ る バ ス ・ 飛 行 機の遅延といったアクシデントに見舞われ、ベルリンのヘルムホルツセンターベルリン 研 究 所 に 到 着 で き た の は 8 日 で し た 。 ド イ ツ で の Sr2RuO4 の実 験 に は 8 日 か ら 参 加 し 、 13 日 の 朝 ま で 続 き ま し た 。 13 日 に ド イ ツ を 出 国 し 、 14 日 に 日 本 へ 帰 国 し ま し た 。 ド イ ツ で も研究所敷地内にあるゲストハウスに宿泊しました。 今回の留学で中性子小角散乱実験に参加できたことを通じて、中性子小角散乱実験の流れやデータの 解析方法、解析に使うアプリケーションの使用方法等を実際に見て学ぶことができ、非常に有意義でした。 また、フランス人、イギリス人、ドイツ人、ウクライナ人など様々な国の人々と共に実験を行い、交流す ることはとても貴重な経験であり、英語力を高めたいという気持ちが強くなりました。自分が作成した試 料(LaNiC2)を中性子散乱で測定することもできたので、より良い試料を作製しようという意欲が高まりま した。 このようにフランス・ドイツでの研究留学は私にとって、とても有意義かつ楽しい体験で、あっとい う間の 2 週間でした。この留学で学んだことを生かしてこれからも研究に励みたいと思います。 このような機会を与えて頂いたことに感謝いたします。ありがとうございました。 1 ② 氏名： 呉 麻美子 1. France (1)BaFe2(As,P)2 At the Institut Laue-Langevin (ILL) in France, our main objective was to conduct small angle neutron scattering (SANS) measurements on BaFe2(As,P)2, which is one of the iron based superconductors with a critical temperature (Tc) of 30 K. After the discovery of iron based superconductors in 2008, intensive worldwide research on this new family of superconductors began. These are type II superconductors with relatively high Tc values. The fundamental mechanism causing the high-temperature superconductivity is still not well understood. SANS experiments on the vortex lattice (VL) of type II superconductors can provide essential information to determine superconducting gap structures, contributing valuable information to the debate regarding the superconducting state of the iron based superconductors. SANS experiments were performed on the instrument D33 at ILL. The crystals of BaFe2(As,P)2 were placed on a sample plate as shown in Figure 1. The sample plates were wrapped with Al foil and attached to the outside of the sample cup (Figure 2). The vortex lattice (VL) was prepared by applying a magnetic field above the Tc and cooling to the base, often whilst applying a small oscillation to the field. Upon establishing a VL signal, the sample and field axis were rotated to fulfill the necessary Bragg conditions in order to image the lattice. The intensity of the scattered neutrons was then investigated as a function of temperature at applied magnetic fields of 0.3 T and 5 T. For measurement at 0.3 T, neutrons with a wavelength of 10 Å were used and the detector was placed 13.4m from the sample. For the measurements at 5 T, neutrons with a wavelength 5 Å were used and the detector was placed at 7.8 m from the sample. Figure 1. Crystals of BaFe2(As,P)2 Figure 2. Samples on a cup The results of these measurements (i.e., the temperature dependence of the scattered intensity at applied magnetic fields of 0.3 T and 5 T) are shown in Figure 3. By analyzing the temperature dependence of the measured intensity, it can be determined whether the superconducting gap is nodal or not. Based on the low-temperature behavior of the obtained data, the appearance of the nodal gap at 0.3 T and the disappearance of nodes at 5 T is expected. Our team performed SANS experiments on BaFe2(As,P)2 several times from 2010 to 2012, and full characterization of the vortex state and gap structure of BaFe2(As,P)2 will be achieved by using additional data obtained from the proposed experiment at ILL. 2 氏名： 0.3T 呉 麻美子 5T Figure 3. Temperature dependence of the scattered intensity (2)LaNiC2 In addition to the analysis of BaFe2(As,P)2, SANS measurements on LaNiC2 were carried out using D33 at ILL . LaNiC2 is one of the superconductors without inversion symmetry that have gained much attention in recent years. Conventional superconductors can only have one spin state either a singlet or triplet, due to Pauli's principle and the law of conservation of parity. However, the superconductors without inversion symmetry can have mixed spin states. Furthermore, in the case of type II superconductors, a new type of vortex state (the so-called helical vortex state) is possible. SANS is an effective technique for exploring this helical vortex state. A sample of LaNiC2 crystal was grown using floating zone method in argon atmosphere with feed rate 20 mm/hour. The Tc of LaNiC2 is 2.7 K and Hc2 is approx. 2000 G. Two pieces of LaNiC2 crystal with a total mass of 0.2346 g were used for the SANS measurements. The crystals on a sample plate are shown in Figure 4. The scattered intensity was measured with an applied magnetic field of 500 G and 1000 G at temperatures of 2.0–2.1 K. Neutrons with wavelengths of 20 Å (for measurements at 500 G) or 12 Å (for measurements at 1000 G) were used. Figure 4: Crystals of LaNiC2 The measurements revealed scattered intensities at appropriate q positions for applied fields of 500 G and 1000 G. This result indicates that LaNiC2 is a material with high potential for studying the helical vortex state. Here, the measurements were done at a temperature approximately 2 K and with a small sample. We can expect to see clearer results when measuring a larger crystal without impurities at lower temperatures. Efforts are continuing to grow single crystals of LaNiC2 in our laboratory and we propose to perform further SANS measurements on LaNiC2 once single crystals of suitable size and quality are achieved. 3 氏名： 呉 麻美子 2. Germany (1)Sr2RuO4 At The Helmholtz Zentrum Berlin (HZB) in Germany, we performed SANS measurements on single crystals of Sr2RuO4. The superconducting phase of Sr2RuO4 has been reported to be a p-wave type, and it has been an attractive material to study p-wave superconductivity. However, some groups claim that there is no credible evidence of p-wave superconductivity in Sr2RuO4 and it might exhibit d-wave superconductivity instead. We proposed SANS measurements on Sr2RuO4 in order to clarify the behavior of a magnetic form factor of the flux lattice line (FLL), F(Q), because anomalous behavior of F(Q) provides strong evidence that Sr2RuO4 shows d-wave superconductivity instead of behavior associated with p-wave superconductors. SANS measurements were performed using the V4 instrument at HZB. The sample crystals were grown using the floating zone method. The Sr2RuO4 crystals on sample plates are shown in Figure 5. The Tc of Sr2RuO4 is 1.5 K and the upper critical field Hc2 is 0.075 T for H// c and 1.5T for H//ab. The magnetic field was applied parallel to the incident neutron beam. At the lowest temperature (0.3 K), the integrated intensity of FLL reflections was measured by rotating the sample angle (omega) and repeated Figure 5. Sr2RuO4 crystals on sample plates this measurement at several different applied magnetic fields. With these measurements, we could obtain the following data for analyzing vortex state of Sr2RuO4. λ[Å] H//ab [T] λ[Å] H//c [T] 0.4 7.08 0.02 8.5 0.7 7.08 0.02 12.74 1 7.08 0.03 14.15 0.7 9.1 Table 1. Measurement condition of Sr2RuO4 Due to problems with importing data into the necessary software application, data analysis remains incomplete. (We have to wait for the release of a new version of the software). We will carefully analyze the data to examine whether there are any VL signals once the problems are fixed. <References> 1. Ruslan Prozorov1 and Russell W Giannetta, Supercond. Sci. Technol. 19 (2006) R41–R67 2. H. Kawano-Furukawa et al. Phys. Rev. B 84, 024507-1 - 024507-9 (2011) 3. Y.Hirose et al. Journal of the Physical Society of Japan 81, 113703-113703-4 (2012) 4. T. Akima et al. Journal of the Physical Society of Japan 68, 694 (1999) 5. Y. Maeno et al. Nature(London) 372,532(1994) 4
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