LPTMC Seminars
The seminars take place in room 523, corridor 12-13, 5th floor.
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Rémy Mosseri (LPTMC)
10.03.2026 10:45 - 11:45SéminairesSalle 523, couloir 12-13, 5è étage
Vers une phyllotaxie tridimensionnelle
Résumé : Inspirés par l'observation de certaines croissances spirales de plantes, les arrangements phyllotactiques bidimensionnels sont des exemples très intéressants de structures homogènes non périodiques engendrées par des règles simples. En séparant les parties radiales et angulaires , ils peuvent par ailleurs être généralisés à des surfaces de courbure positive ou négative. Nous décrirons ici plusieurs essais de généralisation à trois dimensions de ce type d'arrangements. Un premier exemple reprend la modalité de construction des réseaux périodiques compacts à 3D par empilement itérés de réseaux triangulaires sur les espaces interstitiels des couches précédentes. Une seconde approche procède différemment, par croissance radiale, soit de façon automatique en suivant une règle simple, ou bien de façon numérique en minimisant un potentiel d'interaction. Deux autres modèles, pouvant également donner lieu à des structures intéressantes dans R3 seront présentés : un ensemble phyllotactique sur la sphere S3 construit autour d'une fibration de Hopf discrète, et un autre à 4 dimensions obtenu comme produit de deux structures phyllotactiques 2d.
Reference : Some attempts toward 3-dimensional phyllotaxy, Rémy Mosseri and Jean-François Sadoc, Structural chemistry, vol 36, pages 1963–1972 (2025)
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Kilian Fraboulet (Stuttgart)
24.02.2026 10:45 - 11:45SéminairesSalle 523, couloir 12-13, 5è étage
Competing orders in many-electron systems: a renormalization group perspective
The renormalization group is an established approach to study quantum many-body systems, and this applies especially to one of its modern implementations known as the functional renormalization group (FRG). In particular, the FRG constitutes a flexible and unbiased tool for the study of competing orders. In this talk, I will outline recent progress in this direction for correlated electron systems. To this end, I will first discuss the competition between antiferromagnetism, charge density waves and superconductivity in the 2D Hubbard model, thus making a connection with high-temperature superconductors. The special role of bosonization methods will be emphasized along the way. I will also show how the FRG can be combined with dynamical mean-field theory to treat strongly interacting regimes, with a focus on d-wave superconductivity. As a next step, I will increase the complexity of the model by including non-local interactions and discuss unconventional superconductivity in an extended Hubbard model with a connection to moiré materials. Special consideration will also be given to the treatment of retarded interactions with electron-phonon couplings. Finally, I will highlight recent FRG studies of quantum criticality in Dirac materials, with a connection to graphene.
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Ludovic Berthier (ESPCI)
17.02.2026 10:45 - 11:45SéminairesSalle 523, couloir 12-13, 5è étage
Equilibrium phase transition between a fluid and an amorphous solid
When a liquid is cooled, it can form a glass: a mechanically rigid but structurally disordered solid. Experimentally, this transformation occurs when the system falls out of equilibrium and no longer explores all accessible configurations on experimental timescales. A central open question, dating back more than a century, is whether this dynamical arrest reflects an underlying equilibrium phase transition. While theory predicts such a transition in idealized models (with deep connections to spin glass physics), its existence in realistic finite-dimensional systems remains unsettled. I will review this problem and present numerical results for a two-dimensional glass-forming liquid. By combining complementary Monte Carlo techniques, we equilibrate the system down to zero temperature over a range of system sizes and directly measure its equilibrium thermodynamic and structural properties. These results provide evidence for an equilibrium phase transition between a fluid and an amorphous solid. I will conclude by discussing the implications and open questions raised by this finding.