JPS Hokkaido Branch



"Impurity Band Mott Insulators - a new route to (High Tc) Superconductivity"
Prof. G. Baskaran

May 27, 2004

講演題目: Impurity Band Mott Insulators - a new route to (High Tc) Superconductivity
講 師 : Prof. G. Baskaran
     (Institute of Mathematical Sciences, Chennai, India
      および 東北大学金属材料研究所付属 材料科学国際フロンティアセンター・客員教授)
日 時 : 平成16年5月27日 (木) 16:00-
場 所 : 北海道大学大学院理学研究科物理学専攻 大学院講義室 理学部2号館(2-11号室)

要 旨 :
   Mott insulators have given us a nice route to reach a correlation driven high Tc superconductivity and novel superconductors as evidenced by cuprate and organic superconductors. Inspired by a recent finding [1] of superconductivity in boron doped diamond. I suggest that impurity band Mott insulators provide another route for high Tc superconductivity. I will illustrate this idea by going into some details of an electron correlation driven superconductivity mechanism I have suggested for the heavily doped diamond [2]. I argue that the uncompensated boron impurity band is strongly correlated and undergoes a Anderson-Mott insulator to superconductivity transition as the boron density is increased across a critical concentration.
[1] E.A. Ekimov et al., Nature (London), 428 542 (2004)
[2] G. Baskaran, cond-mat/0404286

世話人  熊谷 健一

Category: 支部講演会 | Static URL: /seminar/20040527.htm | Edit

山田 和芳 氏

Dec 16, 2003

講演題目: 高温超伝導は過剰ドーピングによって、どのように消えるのか?
講 師 : 山田 和芳 氏
日 時 : 平成15年12月16日 (火) 16:00-
場 所 : 北海道大学大学院理学研究科物理学専攻 大学院講義室 理学部2号館(2-11号室)

要 旨 :
高温超伝導はモット絶縁体にキャリヤーをドープすることで発現する。しかし過剰にドープすると、超伝導は不安定化し、やがて消えてしまう。従来はいわゆる低ドープ領域での超伝導発現が主に研究されてきたが、最近、La2-xSrxCuO4系の、過剰ドープ領域での中性子散乱を行い、スピン揺らぎや、Cu-Oボンド伸縮モードのフォノンの分散のドープ量依存性を研究した。その結果をもとに、超伝導が過剰ドー プにより、どのように消えていくのかを紹介する。

世話人  熊谷 健一

Category: 支部講演会 | Static URL: /seminar/20031216.htm | Edit

「低スピン単分子磁石の量子ダイナミックス - 三角リングから多面体へ」
野尻 浩之 氏

Nov 18, 2003

講演題目: 低スピン単分子磁石の量子ダイナミックス - 三角リングから多面体へ
講 師 : 野尻 浩之 氏
日 時 : 平成15年11月18日 (火) 16:00-
場 所 : 北海道大学大学院理学研究科物理学専攻 大学院講義室 理学部2号館(2-11号室)

要 旨 :

世話人  熊谷 健一

Category: 支部講演会 | Static URL: /seminar/20031118.htm | Edit

"Tri-refringence, Superprisms, and Pulses-on-the-fly in Photonic Crystal Waveguides"
Prof. Jeremy J. Baumberg

Oct 28, 2003

講演題目: Tri-refringence, Superprisms, and Pulses-on-the-fly in Photonic Crystal Waveguides
講 師 : Prof. Jeremy J. Baumberg
     (Department of Physics & Astronomy, University of Southampton, and Mesophotonics Ltd., Chilworth Science Park,Southampton, S016 7NP, UK)
日 時 : 平成15年10月28日 (火) 17:00-
場 所 : 北海道大学大学院工学研究科 量子物理工学専攻会議室 A3-62

要 旨 :
Photonic Crystal Waveguides promise novel optical functionality in a wide variety of ways due to the considerable modification in optical propagation and interactions induced in these sub-micron periodic structures. Using planar silicon-compatible processing we have produced a wide variety of nanostructured devices over the past few years [1-8] that exhibit high quality photonic bandgap and photonic crystal features. In particular we have gained an understanding of such devices of ultrawide bandwidth ranges allowing us to provide systematic comparison with a variety of our modelling techniques. Recently we have explored how light propagates through photonic crystals by directly tracking the temporal delay of each wavepacket component [1]. In this talk we will discuss a number of the features of photonic crystal waveguides that we are investigating.
[1] "Separation of Photonic Crystal Waveguides Modes using Femtosecond Time-of-Flight", M. C. Netti, C. Finlayson, J. J. Baumberg et al. Appl. Phys. Lett. 81, 3927 (2002).
[2] "Optical Trirefringence in Photonic Crystal Waveguides", M.C. Netti, A. Harris, J.J. Baumberg et al., Phys. Rev. Lett. 86, 1526 (2001).
[3] "Complete and absolute photonic bandgaps in highly symmetric photonic quasicrystals embedded in low refractive index materials", M.E. Zoorob et al., Mat.Sci.Eng.B 74, 168 (2000).
[4] "Experimental investigation of photonic crystal waveguide devices and line-defect waveguide bends", M.D.B. Charlton et al., Mat.Sci.Eng.B 74, 17 (2000).
[5] "Complete photonic bandgaps in 12-fold symmetric quasicrystals", M.E. Zoorob, M.B.D. Charlton, G.J. Parker, J.J. Baumberg and M.C. Netti, Nature 404, 740 (2000).
[6] "Visible Photonic Bandgap Engineering in Silicon Nitride Waveguides", M.C. Netti, M.B.D. Charlton, G.J. Parker, J.J. Baumberg, Appl. Phys. Lett. 76, 991 (2000).
[7] "Guided mode analysis, and fabrication of a 2-dimensional visible photonic band structure confined within a planar semiconductor waveguide", M.D.B. Charlton et al., Mat.Sci.Eng.B 49, 155 (1997).
[8] "Ultra-Broadband Transmission Measurements on Waveguides of Silicon-Rich Silicon Dioxide", RT Neal, CE Finlayson, MC Netti, MDCCharlton, GJ Parker, JJ Baumberg, Appl. Phys. Lett. (2003).

世話人  松田 理

Category: 支部講演会 | Static URL: /seminar/20031028.htm | Edit

Prof. Helmut R. Brand

Oct 14, 2003

講 師 : Prof. Helmut R. Brand
     (Theoretische Physik III, Universitat Bayreuth, 95440 Bayreuth, Germany)
日 時 : 平成15年10月14日 (火) 11:00-
場 所 : 北海道大学大学院理学研究科物理学専攻 大学院講義室 理学部 2号館(2-11号室)

要 旨 :
  Some of the most interesting developments in liquid crystals over the last few years are related to the physical properties of the liquid crystalline phases exhibited by banana-shaped (bent-core) molecules.
  Experimental evidence to date suggests that this is indeed a new sub-field of thermotropic liquid crystals. The biggest challenge is the condensed state known as B7 that grows into the isotropic liquid with many different growth patterns including spirals with both hands. Neither the symmetry nor the physical properties of B7 are understood. A tetrahedratic phase, T, is described by four unit vectors, n1 to n4, oriented along the four tetrahedral corners of a cube. It has the symmetry:
T (- na) = - T ( na) (a = 1,2,3,4);
that is odd under parity. As tetrahedra are not space-filling objects, they can be viewed equally well as precursors of condensed lamellar and/or columnar mesophases. Tetrahedratics are thus a model for studying frustrated lamellar and columnar liquid crystalline phases with many different condensed states that are energetically very close together. In a first step we analyzed the coupling of flow to electric fields and temperature gradients assuming that the symmetry of the tetrahedratic phase is unchanged by the external forces. We also discuss what happens when the tetrahedral angle is allowed to change under the influence of external forces and fields. We also analyze how an external electric field applied to an isotropic tetrahedratic phase can induce orientational order Qij as well as smectic layering. The relation of our analysis to recent experimental observations by Weissflog et al. will be discussed. Work done in collaboration withP.E. Cladis and Harald Pleiner

世話人  北 孝文

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