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Les événements de octobre 2018

séminaire

<p>séminaire</p>
  • Séminaire des doctorants

    • Jeudi 11 octobre 11:00-12:30 - Alice Moutenet - CPHT, Ecole Polytechnique

      Pseudogap and electronic structure of elecron-droped Sr2IrO4

      Résumé : In this talk, I will investigate the effects of correlations on the electronic structure of the Mott insulator Sr2IrO4 upon electron doping, from a theoretical point of view [1]. A rapid collapse of the Mott gap upon doping is found, and the electronic structure displays a strong momentum-space differentiation at low doping level : The Fermi surface consists of pockets centered around (π/2,π/2), while a pseudogap opens near (π,0). The pseudogap closes upon increasing doping, but a differentiated regime characterized by a modulation of the spectral intensity along the Fermi surface persists to higher doping levels. These results, obtained within the cellular dynamical mean-field-theory framework, are discussed in comparison to recent photoemission experiments [2,3,4] and an overall good agreement is found.
      [1] A. Moutenet, A. Georges, and M. Ferrero, PRB 97 155109 (2018).
      [2] Y.K. Kim, O. Krupin, J.D. Denlinger, A. Bostwick, E. Rotenberg, Q. Zhao, J. F. Mitchell, J. W. Allen, and B. J. Kim, Science 345, 187 (2014).
      [3] V. Brouet, J. Mansart, L. Perfetti, C. Piovera, I. Vobornik, P. Le Fèvre, F. Bertran, S. C. Riggs, M. C. Shapiro, P. Giraldo-Gallo, and I. R. Fisher, PRB 92, 081117(R) (2015).
      [4] A. de la Torre, S. McKeown Walker, F. Y. Bruno, S. Riccó, Z. Wang, I. Gutierrez Lezama, G. Scheerer, G. Giriat, D. Jaccard, C. Berthod, T. K. Kim, M. Hoesch, E. C. Hunter, R. S. Perry, A. Tamai, and F. Baumberger, PRL 115, 176402 (2015).

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

      Article

  • Séminaire des doctorants

    • Jeudi 18 octobre 11:00-12:00 - Andrzej Ptok - Polish Academy of Sciences, Krakow

      Unconventional superconductivity in iron-based superconductors

      Résumé : Iron-based superconductors exhibit many interesting features. One of them are discontinuous phase transition from superconducting to normal state in low temperature, characteristic of the materials in which we can expect the existence of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase [1]. In this seminar we discuss possibility of the realization of this exotic phase in multi-bands iron-based superconductors [2]. Moreover, it will be demonstrated that such FFLO instability may be explored through the static Cooper pair susceptibility renormalized by pairing interaction. We will present an efficient method of its evaluation using Wannier orbitals derived from ab initio (DFT) calculation. We will discuss applications of these techniques to the heavy fermion compound CeCoIn5 and to iron based superconductors FeSe [3]. We also discuss consequences concerning the existence of a FFLO phase in multi-band iron based superconductors [4].
      [1] D. A. Zocco et al., Phys. Rev. Lett. 111, 057007 (2013) ; Ch.-w. Cho et al., Phys. Rev. Lett. 119, 217002 (2017). [2] A. Ptok and D. Crivelli, J. Low Temp. Phys. 172, 226 (2013) ; A. Ptok, Eur. Phys. J. B 87, 2 (2014). [3] A. Ptok, K. J. Kapcia, P. Piekarz and A. M. Oleś, New J. Phys. 19, 063039 (2017). [4] A. Ptok, J. Phys. : Condens. Matter 27, 482001 (2015).

      Lieu : Moyen Amphi RDC @ LPS, bât 510

      Article

  • Séminaire des doctorants

    • Mardi 23 octobre 11:00-12:30 - Walter Escoffier - LNCMI Toulouse

      Non 1/B-periodic Shubnikov-de Haas oscillations in gate tunable 2DEG at the LaAlO3/SrTiO3 interface

      Résumé : The formation of a two-dimensional electron gas (2DEG) at the interface between two insulators SrTiO3 (STO) and LaAlO3 (LAO) is among the most intriguing finding in oxide electronics. In recent years, several exotic phenomena including super-conductivity [1], Rashba spin-orbit coupling [2], ferromagnetism and quantum oscillations [3] have been reported at this interface. While the theoretical calculations for band structure reveal the formation of several subbands (dxy, dxz and dyz) arising from the interface crystal field splitting of Ti:3d t2g orbital, no clear consensus has been reached yet from experimental evidences. Here, I investigate the quantum transport of a high mobility 2DEG at LAO/STO interface under high magnetic field (55T). Surprisingly, the Shubnikov-de Haas oscillations (SdHO) of the longitudinal resistance (Rxx) are aperiodic when plotted as a function of inverse magnetic field. This observation, at the origin of a non-linear Landau fan diagram, contrasts with a linear Hall resistance (Rxy) over the full magnetic field range. In this seminar, I will explore different scenarios to explain the peculiar transport properties of such 2DEG at LAO/STO interface. In particular, I will show that the Roth-Gao-Niu model [4], where the phase of the magnetic oscillations depends both on energy and magnetic field, provides a natural explanation of the experimental results.
      [1] A. Joshua et al., Nature Comm. 3, 1129 (2012) ; J. Biscaras et al., Phys. Rev. Lett. 108, 247004 (2012). [2] A. D. Caviglia et al., Phys. Rev. Lett. 104, 126803 (2010) ; Z. Zhong et al., Phys. Rev. B 87, 161102(R) (2013). [3] B. Shalom et al., Phys. Rev. Lett. 105, 206401 (2010) ; M. Yang et al., App. Phys. Lett. 109, 122106 (2016). [4] Y. Gao and Q. Niu, PNAS 114, 7295 (2017) ; J.N. Fuchs et al., 4 024 (2018).

      Lieu : Moyen Amphi RDC @ LPS, bât 510

      Article

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