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The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community.   [ More information ]

Upcoming Seminars at LPENS
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Wednesday 27 October 2021, 14:00 at LPENS, L367
( onsite+zoom. For zoom meeting id, write to )
FORUM-ENS (Forum de Physique Statistique @ ENS) cond-mat.stat-mech
Karyn Le Hur ( CPHT-X ) Geometry, Light Response and Quantum Transport in Topological States
Abstract: Topological states of matter are characterised by a gap in the bulk of the system referring to an insulator or a superconductor and topological edge modes as well which find various applications in transport and spintronics. The bulk-edge correspondence is associated to a topological number. The table of topological states include the quantum Hall effect and the quantum anomalous Hall effect, topological insulators and topological superconductors in various dimensions and lattice geometries. Here, we discuss classes of states which can be understood from mapping onto a spin-1/2 particle in the reciprocal space of wave-vectors. We develop a geometrical approach on the associated Poincare- Bloch sphere, developing smooth fields, which shows that the topology can be encoded from the poles only. We show applications for the light-matter coupling when coupling to circular polarisations and develop a relation with quantum transport and the quantum Hall conductivity. The formalism allows us to include interaction effects. We show our recent developments on a stochastic approach to englobe these interaction effects and discuss applications for the Mott transition of the Haldane and Kane-Mele models. Then, we develop a model of coupled spheres and show the possibility of fractional topological numbers as a result of interactions between spheres and entanglement allowing a superposition of two geometries, one encircling a topological charge and one revealing a Bell or EPR pair. Then, we show applications of the fractional topological numbers C=1/2 in bilayer honeycomb models describing topological semi-metals characterised by a quantised $\pi$ Berry phase at one Dirac point.

Monday 8 November 2021, 13:30 at LPENS, Online - Zoom - ID de réunion : 971 0761 8272 - Code secret : 0811 LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
Alexander Högele ( LMU ) Excitons in van der Waals heterostructures
Abstract: Van der Waals crystals of two-dimensional semiconductors have evolved as an increasingly significant material platform for condensed matter research. Using exfoliated monolayers, a wide range of vertical van der Waals heterostructures can be assembled into rationally designed material systems with tailored optical properties of strongly bound excitons. In my talk, I will discuss the results of our recent studies of various van der Waals heterostructure assemblies and highlight the roles of layer constituents, number, twist angle and atomic registry.

Monday 22 November 2021, 13:30 at LPENS, Salle Djebar - 29 rue d'Ulm LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
Caglar Girit ( Collège de France ) TBA

Wednesday 8 December 2021, 14:30 at LPENS, L367 FORUM-ENS (Forum de Physique Statistique @ ENS) cond-mat.stat-mech
Varda Faghir Hagh ( The University of Chicago ) Free-then-freeze: transient learning degrees of freedom for introducing function in materials
Abstract: Many protocols used in material design and training have a common theme: they introduce new “learning’’ degrees of freedom, often by relaxing away existing constraints, and then evolve these degrees of freedom based on a rule that leads the material to a desired state at which point these learning degrees of freedom are frozen out. Using this conceptual framework, we first introduce and subsequently remove different sets of degrees of freedom from the energy minimization process of athermal particle packings. By doing so, we are able to create stable jammed packings that exist in exceptionally deep energy minima marked by the absence of low-frequency quasilocalized modes; this added stability persists in the thermodynamic limit. We show that the inclusion of particle radii as learning degrees of freedom leads to deeper and much more stable minima than does the inclusion of particle stiffnesses. This is because particle radii couple to the jamming transition whereas stiffnesses do not. Thus different choices for the learning degrees of freedom can lead to very different training outcomes.

Monday 13 December 2021, 13:30 at LPENS, Salle Djebar - 29 rue d'Ulm LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
Anaïs Dréau ( Laboratoire Charles Coulomb, L2C ) TBA

Monday 17 January 2022, 13:30 at LPENS, TBA LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
Nicolas Roch ( Institut Néel, Grenoble ) TBA

Monday 31 January 2022, 13:30 at LPENS, TBA LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
François Dubin ( Institut des Nansciences de Paris, INSP ) TBA

Monday 14 March 2022, 13:30 at LPENS, TBA LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
Rebeca Ribeiro ( Centre de Nanosciences et de Nanotechnologies, C2N ) TBA

seminars from series at institute
in subject with field matching

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