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Les événements de janvier 2019

séminaire

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

    • Jeudi 10 janvier 11:00-12:30 - Marco Polini - IIT-Genova et Université de Manchester

      Failure of conductance quantization in two-dimensional topological insulators due to non-magnetic impurities

      Résumé : Despite topological protection and the absence of magnetic impurities, two-dimensional topological insulators display quantized conductance only in surprisingly short channels, which can be as short as 100 nm for atomically-thin materials. We show that the combined action of short-range non-magnetic impurities located near the edges and onsite electron-electron interactions effectively creates non-collinear magnetic scatterers, and, hence, results in strong back-scattering. The mechanism causes deviations from quantization even at zero temperature and for a modest strength of electron-electron interactions. Our theory provides a straightforward conceptual framework to explain experimental results, especially those in atomically-thin crystals, plagued with short-range edge disorder.

      Lieu : Moyen Amphi RDC @ LPS, bât 510

      Article

  • Séminaire des doctorants

    • Vendredi 11 janvier 11:00-12:30 - Carol Aguiar - UFMG Belo Horizonte

      Light cone effect and manipulation of energy current in spin systems

      Résumé : In this seminar, I will consider one dimensional systems of quantum spins that interact when in neighboring sites and are described by the Heisenberg XXZ model. I will show results of two recent works of our research group. In the first work, we study the non-equilibrium dynamics observed after connecting two XXZ chains, one initially prepared in the ferromagnetic phase and the other in the paramagnetic phase. When analyzing the magnetization and the entanglement entropy as a function of time and the chain site, we observe an effective light cone. In other words, there is a limit in the speed with which information propagates, which I will show to be related to different excitations of the equilibrium case. In the second work, we couple magnetic reservoirs to the edges of a spin chain in which the spin coupling in the z-direction varies gradually along the chain. We analyze the spin and energy currents through the chain when the non-equilibrium steady state is reached. According to our results, it is possible to manipulate the behavior of the energy current by applying an external magnetic field
      that also varies along the chain.

      Lieu : salle 315, aîle sud LPS, bât 510

      Article

  • Séminaire des doctorants

    • Jeudi 24 janvier 11:00-12:00 - Mathieu Istas - CEA Inac- Grenoble

      Computing quantum transport in 2 or 3 dimensions for nearly translationally invariant devices

      Résumé : In this talk, I will present a method to compute quantum transport in neraly translationnally invariant systems in 2D or 3D. A short introduction will be dedicated to the Kwant software and the rest will be focused on the one of the novelties that will be included in future versions. While Kwant use the scattering matrix approach to simulate transport in quasi-1D system, I used the Green’s function approach to simulate infinite or semi-infinite systems in 2D or 3D. Using the Dyson equation, it is possible to add local impurities, hoppings, and even impurities invariant by translation. I will show a few examples, from benchmarking in 2D with graphene to systems that are out of reach with usual methods like transport in Weyl semimetals across impurities.

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

      Article

  • Séminaire des doctorants

    • Jeudi 31 janvier 11:00-12:00 - Manuel Houzet - CEA- Grenoble

      Coulomb blockade of a nearly-open Majorana island

      Résumé : We elucidate the nature of the suppression of Coulomb blockade in a nearly-open system made of topological superconductors. The topological superconductors are characterized by a finite gap in the energy spectrum, coexisting with a nontrivial degeneracy of the ground state, which causes the periodicity in the induced charge to be e and not 2e. This difference in the states and spectra from both conventional superconductors and normal metals results in a different underlying physics of the disappearance of Coulomb blockade oscillations at perfect transmission. We show that it is related to the physics of adiabatic transitions between a discrete state and a continuum of itinerant states. We formulate a quantitative theory valid for the crossover from a regime where the amplitude of Coulomb blockade oscillations is proportional to the reflection amplitude, to a regime where the physics is similar to a conventional Cooper-pair box in the transmon regime.

      Lieu : Moyen Amphi RDC @ LPS, bât 510

      Article

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