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Les événements de avril 2018


  • Séminaire des doctorants

    • Mardi 10 avril 14:00-15:00 - Brian Skinner - MIT's Research Laboratory of Electronics

      Semimetals Unlimited : Unbounded electrical and thermal transport properties in nodal semimetals

      Résumé : Modern electronics is built on semiconductors, whose utility comes from their ability to operate on either side of the conductor-insulator dichotomy. For practical applications, however, semiconductors face certain unavoidable limitations imposed by the physics of Anderson localization and by the disorder introduced through doping. In this talk I discuss whether these same limitations apply to nodal semimetals, which are a novel class of three-dimensional materials that have a vanishing density of states (like insulators) but no gap to electron-hole excitations (like conductors). I show that, surprisingly, in a certain class of nodal semimetals the electronic mobility can far exceed the bounds that constrain doped semiconductors, becoming divergingly large even with a finite concentration of charged impurities. I then discuss the thermoelectric effect in semimetals, and show that their electron-hole symmetry allows for a thermopower that grows without bound under the application of a strong magnetic field. This large thermopower apparently enables the development of devices with record-large thermoelectric figure of merit.

      Lieu : salle 208a, aîle sud LPS, bât 510


  • Séminaire des doctorants

    • Lundi 16 avril 11:00-12:00 - Andres Cano - Institut Néel

      FeSi : a novel building-block for iron-based superconductivity

      Résumé : Iron-based superconductors represent the latest family of high-temperature unconventional superconductors [1]. In these systems, the Fe atom is invariably associated to pnictogen (As, P) or chalcogen (Se, S, Te) elements, with the only and intensively debated exception of YFe2Ge2 [2,3]. This circumstance raises the important fundamental question about the link between Fe-based superconductivity and the apparent need of these pnictogens and chalcogens [3]. At the same time, to escape from such harmful and/or comparatively scarce As- or Se-like elements is highly desirable for applications.
      In the talk I will introduce the new material LaFeSiH, which is first silicide that surpasses traditional pnictide and chalcogenide compounds as Fe-based superconductors, and discuss some of its physical properties [4]. These include superconductivity with onset at 11 K, and its coexistence with antiferromagnetic order and orthorhombic distortion already in the parent phase.
      [1] See e.g. H. Alloul and A. Cano (Guest Editors), Iron-based superconductors, C. R. Physique 17, 1 (2016) ; and the references therein.
      [2] J. Chen et al., Unconventional Superconductivity in the Layered Iron Germanide YFe2Ge2, PRL 116, 127001 (2016).
      [3] H. Kim et al., Crystal growth and annealing study of fragile, non-bulk superconductivity in YFe2Ge2, Phil. Mag. 95, 804 (2015) ; D. Guterding et al., Nontrivial Role of Interlayer Cation States in Iron-Based Superconductors, PRL 118, 017204 (2017).
      [4] F. Bernardini, G. Garbarino, A. Sulpice, M. Núñez-Regueiro, E. Gaudin, B. Chevalier, A. Cano, and S. Tencé, Iron-based superconductivity extended to the novel silicide hydride LaFeSiH, PRB 97 100504(R) (2018).

      Lieu : salle 315 3eme étage, aîle sud LPS, bât 510


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