「Overview of two multiferroic systems: RMnO3 and BiFeO3」
Je-Geun Park　氏

Feb 02, 2016

日本物理学会北海道支部講演会

講演題目：　Overview of two multiferroic systems: RMnO3 and BiFeO3
講　師　：　Je-Geun Park　博士
　　　　　Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul National University
日　時　：　平成28年2月2日 (火) 16:30-18:00
場　所　：　北海道大学 理学部５号館 (5-205室)

要　旨　：
Multiferroic materials that have the coexistence of both magnetic and ferroelectric ground states have drawn significant attention in materials science over the past ten years or so. The underlying origin of this unusual behavior in either naturally occurring materials or artificially synthesized thin films has been a strong enough motivation for material scientists to discover or rediscover new multiferroic materials. Among a long list of multiferroic materials, hexagonal manganites RMnO3 and BiFeO3 are arguably two most interesting multiferroic materials. In particular, BiFeO3 has been extensively investigated for potential applications by virtue of its magnetic and ferroelectric transitions occurring above room temperature: TN=650 K and TC=1050 K. Moreover, it has a very interesting incommensurate magnetic phase transition with an extremely long period of 650 A. On the other hand, the hexagonal manganite materials exhibit a natural two-dimensional triangular lattice, which provide an interesting platform to investigate low dimensional magnetism with a supposedly strong coupling to the ferroelectric order parameter. Over the past few years or so, there have been a multitude of studies done on both compounds. Largely thanks to these extensive studies, we have now come to know extremely details about the physical properties of the two materials. In this talk, I will present our results obtained from high resolution neutron scattering experiments on these two fascinating materials. [1] Seongsu Lee, et al., Nature 451, 805 (2008) [2] Jaehong Jeong, et al., Phys. Rev. Lett. 108, 077202 (2012) [3] Joosung Oh, et al., Phys. Rev. Lett. 111, 257202 (2013) [4] Jaehong Jeong, et al., Phys. Rev. Lett. 113, 107202 (2014) [5] [Topical Review] Je-Geun Park, et al., J. Phys.: Condens. Matter 26, 433202 (2014) [6] [Invited feature article] Hasung Sim, Joosung Oh, Jaehong, Jeong, Manh Duc Le, and Je-Geun Park, Acta. Crystallog. B (in press): arXiv:1511.04181

世話人　 網塚浩
（amiami@phys.sci.hokudai.ac.jp）
北海道大学理学部物理学科　(電話011-706-3484)

「Subgap states in disordered superconductors with strong magnetic impurities」
Yakov V. Fominov　氏

Jan 18, 2016

日本物理学会北海道支部講演会

講演題目：　Subgap states in disordered superconductors with strong magnetic impurities
講　師　：　Yakov V. Fominov　博士
　　　　　L. D. Landau Institute for Theoretical Physics
日　時　：　平成28年1月18日 (月) 16:30-18:00
場　所　：　北海道大学 工学部 物理工学系大会議室 (A1-17室)

要　旨　：
We study the density of states (DOS) in diffusive superconductors with point-like magnetic impurities of arbitrary strength described by the Poissonian statistics. The mean-field theory predicts a nontrivial structure of the DOS with the continuum of quasiparticle states and (possibly) the impurity band. In this approximation, all the spectral edges are hard, marking distinct boundaries between spectral regions of finite and zero DOS. Considering instantons in the replica sigma-model technique, we calculate the average DOS beyond the mean-field level and determine the smearing of the spectral edges due interplay of fluctuations of potential and non-potential disorder. The latter, represented by inhomogeneity in the concentration of magnetic impurities, affects the subgap DOS in two ways: via fluctuations of the pair-breaking strength and via induced fluctuations of the order parameter. In limiting cases, we reproduce previously reported results for the subgap DOS in disordered superconductors with strong magnetic impurities.

世話人　 浅野　泰寛
（asano@eng.hokudai.ac.jp）
北海道大学工学部応用理工系学科　(電話011-706-6115)

「薄いキラル液晶セルが発現する特異な秩序構造」
福田 順一　氏

Nov 26, 2015

日本物理学会北海道支部講演会

講演題目：　薄いキラル液晶セルが発現する特異な秩序構造
講　師　：　福田 順一　博士
　　　　　産業技術総合研究所 主任研究員
日　時　：　平成27年11月26日 (木) 16:30-17:30
場　所　：　北海道大学工学部物理工学系大会議室 (A1-17室)

要　旨　：
鏡映対称性を持たないキラルな液晶は，自発的な配向ねじれ変形などの様々な自己組織的な秩序構造を形成する．その例の1つに，液晶配向の線欠陥が3次元的に配置して数百ナノメートル程度の周期的構造を示す，コレステリックブルー相と呼ばれる秩序相が存在する．本研究では，連続体理論に基づいた数値計算によって，そのようなコレステリックブルー相を示すキラル液晶を，2枚の平行平板からなる薄いセル（ここで言う「薄い」とは，構造の周期程度以下のことである）内での挙動を調べた．その結果，セル表面と液晶配向の相互作用（アンカリング）によって生じるフラストレーションにより，セル内の液晶はバルクのコレステリックブルー相とは全く異なる様々な秩序構造を示すことが明らかとなった．その中には，様々な凝縮系において発現することが明らかとなっているスカーミオン（中心に特異点を有しない渦状の構造）からなる6回対称格子も含まれる．また時間があれば，それらの秩序構造が示す光学的性質（特にどのように光を反射するか）について行なった数値計算についても紹介する。 (参考論文) J. Fukuda and S. Zumer, Phys. Rev. Lett. 104, 017801 (2010); Phys. Rev.Lett. 106, 097801 (2011); Nature Commun. 2, 246 (2011); Mol. Cryst. Liq.Cryst. 594, 70 (2014). The high-pressure technique has been recognized as one of the powerful tools

世話人　 折原宏

北海道大学工学部応用理工系学科　(電話011-706-6115)

「Role of pressure on Critical Behavior of some Perovskite Manganites」
Prof. S. Arumugam　氏

Oct 13, 2015

日本物理学会北海道支部講演会

講演題目：　Role of pressure on Critical Behavior of some Perovskite Manganites
講　師　：　Prof. S. Arumugam
　　　　　Centre for High Pressure Research, School of Physics, Bharathidasan University, India
日　時　：　平成27年10月13日 (火) 16:00-17:00
場　所　：　室蘭工業大学 教育・研究1号館A棟 A322（電気電子系セミナー室）

要　旨　：
The high-pressure technique has been recognized as one of the powerful tools to investigate the physical properties of solids because pressure can vary physical parameters cleanly, not introducing disorder. High pressure, which effectively increases the electron transfer interaction or the one electron band-width, is a powerful tool for investigation of the electronic and magnetic properties of manganites. In this lecture, few results on critical behavior of cubic perovskites under pressure and magnetic field will be discussed. Hydrostatic pressure dependence of the order of phase transition in (Sm0.7Nd0.3)0.52Sr0.48MnO3, La0.4Bi0.3Sr0.3MnO3 and Pr0.6Ca0.4Mn0.96B0.04O3 (B = Co and Cr) systems were analyzed. At ambient pressure, these systems undergo a first-order paramagnetic insulator to ferromagnetic-metallic phase transition. The application of pressure on magnetization of (Sm0.7Nd0.3)0.52Sr0.48MnO3 and La0.4Bi0.3Sr0.3MnO3 systems suppress the first-order paramagnetic to ferromagnetic, and leads the second-order one under 1.21 and 0.91 GPa. Similarly, first-second order crossover takes place, are 2.02 and 2.40 GPa for Co and Cr doped samples respectively. In order to understand the nature of ferromagnetism in second order transition, it is essential to determine the critical values, and the assigning them for existing theoretical models such as mean-field, tricritical, Heisenberg and 3D Heisenberg etc., Here, the estimated values for (Sm0.7Nd0.3)0.52Sr0.48MnO3 and Pr0.6Ca0.4Mn0.96Co0.04O3 are close to the 3D Heisenberg model for the Co doped sample suggesting short-range FM interaction. On the other hand, the estimated values for La0.4Bi0.3Sr0.3MnO3 and Pr0.6Ca0.4Mn0.96Cr0.04O3 are close to the 3D Heisenberg model for the Co doped sample suggesting long-range interaction.

世話人　 関根ちひろ
（sekine@mmm.muroran-it.ac.jp）
室蘭工業大学情報電子工学系学科　(電話0143-46-5000)

「Influence of noise on dissipative solitons and their interaction」
Prof. Dr. Helmut R. Brand

Sep 08, 2015

日本物理学会北海道支部講演会

講演題目：　Influence of noise on dissipative solitons and their interaction
講　師　：　Prof. Dr. Helmut R. Brand
　　　　　Department of Physics, University of Bayreuth, Germany
日　時　：　平成27年9月8日 (火) 13:00-14:00
場　所　：　北海道大学理学部2号館404室

要　旨　：
We give an overview on the influence of noise on spatially localized patterns and their interaction. Localized patterns include stationary dissipative solitons, oscillatory dissipative solitons with one and two frequencies as well as exploding dissipative solitons. The influence of noise on spatially localized structures of arbitrary length, which are localized due to the trapping mechanism [1], has been investigated and it was shown that the logarithm of the lifetime scales inversely with the noise intensity. Thus the picture of a noise activated barrier crossing has been demonstrated [1]. A long standing puzzle in the field of pattern formation has been the observation of the partial annihilation of pulses in binary fluid convection [2] and during CO oxidation in surface reactions [3,4]. In [5] it has been shown that already a small amount of additive noise can account for the observations. The mechanism will be elucidated in the presentation. Recently it has been shown that a small amount of noise can induce explosions for dissipative solitons in the vicinity of the transition sequence from stationary dissipative solitons to exploding dissipative solitons via three different routes [6]. Finally we will also comment on the effect of large noise in connection with dissipative solitons [7]. [1] H. Sakaguchi, H.R. Brand, Physica D - Nonlinear Phenomena 97, 274 (1996). [2] P. Kolodner, Phys. Rev. A44, 6466 (1991). [3] H.H. Rotermund, S. Jakubith, A. von Oertzen, G. Ertl, Phys. Rev. Lett.66, 3083 (1991). [4] A. von Oertzen, A.S. Mikhailov, H.H. Rotermund, G. Ertl, J. Phys.Chem. B102, 4966 (1998). [5] O. Descalzi, J. Cisternas, D. Escaff, H.R. Brand, Phys. Rev. Lett.102, 188302 (2009). [6] C. Cartes, O. Descalzi, H.R. Brand, Phys. Rev. E 85, 015205 (2012). [7] O. Descalzi, C. Cartes, H.R. Brand, Phys. Rev. E 91, 020901 (2015).

世話人　 北　孝文
（kita@phys.sci.hokudai.ac.jp）
北海道大学理学部物理学科　(電話011-706-3484)