「Nematic superconductivity in topological materials」
Anne de Visser 氏

Oct 21, 2019


講演題目: Nematic superconductivity in topological materials
講 師 : Anne de Visser 氏
      Van der Waals-Zeeman Institute, University of Amsterdam, The Netherland
日 時 : 2019年10月21日 (月) 16:30 - 17:30
場 所 : 北海道大学理学部5号館5-206
要 旨 :
Topological insulators have generated a wide research interest, because they offer access to novel quantum states with unprecedented properties. Most interestingly, the concept of topological insulators can be transferred to superconductors, where the superconducting gap plays the role of the band gap of the insulator. Topological superconductors are predicted to have an exotic Cooper-pair state in the bulk and gapless Andreev bound states at the surface (Majorana modes), and therefore offer new, challenging routes to test theories of unconventional superconductivity. In this presentation I will focus on the recent developments in superconducting Bi2Se3-based crystals, where field-angle dependent measurements of the transport, thermal and magnetic properties have revealed a spontaneous breaking of the rotational symmetry [1,2,3]. The rotational symmetry breaking in the macroscopic superconducting properties is explained in terms of nematic superconductivity, that is associated with a two-component superconducting order parameter (Eu representation) [4]. The experimental results provide solid evidence for unconventional superconductivity with an odd-parity spin-polarized triplet Cooper-pair state (Δ4-pairing),that was recently proposed for rhombohedral topological superconductors [5].

[1] Y. Pan et al., Sci. Rep. 6, 28632 (2016).
[2] S. Yonezawa et al., Nature Phys. 13, 123 (2017).
[3] T. Asaba et al., Phys. Rev. X 7, 011009 (2017).
[4] J. Venderbos et al., Phys. Rev. B 94, 180504R (2016).
[5] L. Fu, Phys. Rev. B 90, 100509R (2014).

世話人 網塚 浩

(北海道大学大学院理学研究院 物理学部門)

Category: 支部講演会 | Static URL: /seminar/20191021.htm | Edit

「密度行列のダイナミクスにおける非エルミート行列の例外点 」
羽田野 直道 氏

Oct 15, 2019


講演題目: 放射光X線と中性子散乱の相補利用を通した局所反転対称性のないf電子系 化合物の研究
講 師 : 羽田野 直道 氏
      東京大学 生産技術研究所
日 時 : 令和元(2019)年10月15日(火) 13:30〜
場 所 : 北海道大学工学部A棟 A1-17
要 旨 :
[1] N. Hatano, Exceptional points of the Lindblad operator of a two-level system, Mol. Phys. 117, 2121--2127 (2019)

世話人 小布施 秀明


Category: 支部講演会 | Static URL: /seminar/20191015.htm | Edit

「Experimental signature of the attractive Coulomb force between positive and negative magnetic monopoles in spin ice」
Carley PAULSEN 氏

Oct 02, 2019


講演題目: Experimental signature of the attractive Coulomb force between positive and negative magnetic monopoles in spin ice
講 師 : Carley PAULSEN 氏
      Institute of Neel, CNRS, Grenoble, France, Director of Research
日 時 : 令和元年10月2日 (水) 10:30~11:30
場 所 : 室蘭工業大学 教育研究1号館 A324 室
要 旨 :
Thermal physics, electrical engineering, chemistry and biochemistry are essentially determined by the Coulomb interaction of quasiparticles. Such quasiparticles are not real and cannot be interrogated by the methods of particle physics. So how do you prove experimentally that two quasiparticles interact via Coulomb’s law ? In this talk I will show how this can be done for magnetic, rather than electric quasiparticles. By freezing spin ice to 65 mK we create (+ -) pairs of emergent magnetic monopoles which we then separate with a magnetic field. Our experiment is arranged to make the magnetic current exactly analogous to an electrical current, and we observe a current that grows exponentially with the square root of the applied field. A non-Ohmic current that grows exponentially with the square root of applied electric field is well known from thermionic emission, electrolytes and semiconductors. It is a universal signature of the attractive Coulomb force between positive and negative electrical charges, which is revealed as the charges are driven in opposite directions by the force of an applied electric field.
世話人  関根 ちひろ

Category: 支部講演会 | Static URL: /seminar/20191002.htm | Edit
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