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Les événements de octobre 2017

séminaire

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

    • Jeudi 12 octobre 11:00-12:00 - Dganit Meidan - Ben-Gurion University

      Interactions and disorder in topological superconducting wires

      Résumé : The prospects of building quantum devices based on topologically ordered states of matter has caused a great deal of excitement. In these systems, emergent excitations known as Majorana zero modes that occur at sample edges obey non- Abelian exchange statistics, and their manipulation is inherently protected from common sources of decoherence. While their existence is known to be reasonably stable to imperfect conditions such as impurities and weak electron- electron interactions, aspirations to observe and manipulate Majorana zero-modes in proximity coupled systems requires a detailed study of both these effects. As a particular example we numerically study the effect of disorder on the stability of the many body zero mode in a Kitaev chain with local interactions. Our numerical procedure allows us to resolve the position-space and multi-particle structure of the zero modes, as well as providing estimates for the mean energy splitting between pairs of states of opposite fermion parity, over the full many body spectrum. We find that the parameter space of a clean system can be divided into regions where interaction induced decay transitions are suppressed (Region I) and where they are not (Region II). In Region I we observe that disorder has an adverse effect on the zero mode, which extends further into the bulk and is accompanied by an increased energy splitting between pairs of states of opposite parity. Conversely Region II sees a more intricate effect of disorder showing an enhancement of localization at the system’s end, accompanied by a reduction in the mean pairwise energy splitting

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

      Article

  • Séminaire des doctorants

    • Jeudi 19 octobre 11:00-12:00 - Christopher Reeg - Basel

      Proximity-induced superconductivity in single and double Majorana nanowires

      Résumé : In this talk, we will discuss various aspects of the superconducting proximity effect as it pertains to realizing topological superconductivity in both one- and two-nanowire systems. As experimental setups have moved almost exclusively toward inducing superconductivity in nanowires using a thin ( 10 nm thickness) layer of Al which forms a very strong contact, we will first discuss the influence of the finite thickness of the superconductor on the proximity effect. We will show that due to the large level spacing in Al, a large tunneling energy is required in order to reach the strong-coupling limit observed experimentally. However, we also show that such strong coupling induces a large shift in the effective chemical potential of the nanowire which pushes the topological threshold to magnetic field strengths greatly exceeding the critical field of Al. Next, we will show that intrawire and interwire pairing interfere destructively with one another in a double-nanowire system, and that this destructive interference can be utilized to significantly reduce the magnetic field threshold required to reach the topological phase. We will also discuss how to engineer (effective) Kramers pairs of Majorana fermions in double nanowires when time-reversal symmetry is explicitly broken.

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

      Article

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