Seconde journée thématique sur le thème de la renormalisation le lundi 12 juin à l'Ecole Polytechnique, Amphi Curie

https://indico.math.cnrs.fr/e/themaRenormalisation12juin2023

Orateurs

Nils Berglund (université d'Orléans, institut Denis Poisson)

Jonas Lampart (Université de Bourgogne, laboratoire UCB)

Slava Rychkov (IHES)

Monday 15/05 at 14:00

Conference room Louis Michel (CPHT)

Marc-Olivier Renou (Inria and CPHT)

Bell theorem and its generalization: From foundations to applications

Abstract: Quantum correlations are obtained when multiple parties perform independent measurements on a shared quantum state. Bell’s seminal theorem proves that certain correlations predicted by quantum theory resist explanations in terms of any Local Hidden Variable theory based on shared randomness. I’ll first review the Bell theorem, its main foundational consequences and some of its applications. Then, I will discuss recent generalization of this theorem in the context of causal quantum networks, in which now multiple parties perform independent measurements on several, independent quantum states.

Tuesday 02/05 at 14:00

Conference room Louis Michel (CPHT)

Matteo Crispino (ESPCI Paris)

Slave-spin mean field for broken-symmetry states: Néel antiferromagnetism and its phase separation in multi-orbital Hubbard models

Abstract: We introduce the generalization of the Slave-Spin Mean-Field method to broken-symmetry phases. Through a variational approach we derive the single-particle energy shift in the mean-field equations which generates the appropriate self-consistent field responsible for the stabilization of the broken symmetry. With this correction the different flavours of the slave-spin mean-field are actually the same method and they give identical results to Kotliar-Ruckenstein slave-bosons and to the Gutzwiller approximation. We apply our formalism to the Néel antiferromagnetic state and study it in multi-orbital models as a function of the number of orbitals and Hund's coupling strength, providing phase diagrams in the interaction-doping plane. We show that the doped antiferromagnet in proximity of half-filling is typically unstable towards insulator-metal and magnetic-non magnetic phase separation. Hund's coupling extends the range of this antiferromagnet, and favors its phase separation.

L’aménagement du patio avance bien. Nous avons déjà notre petit verger (pommiers, poiriers, figuier…), et surtout de la terre qui est préparée pour les plantations, nous avons 5 parcelles prêtes à l’emploi qui n’attendent que nous !

Vendredi 21 avril à 13h15  réunion mensuelle dans le patio

C’est une réunion très importante car nous devons décider :

- Qu’est-ce que nous allons planter ? (tomates ? concombres ? pommes de terres ? herbes aromatiques ? herbes médicinales ? etc)

- Comment nous allons planter sur 5 parcelles ? Parcelles thématiques (ex. : légumes ; herbes …) ? Parcelles par famille botanique (ex : Cucurbitacées …) ? Autre ?

- Quand allons-nous planter ? Nous devons établir un planning de plantation. Les jardiniers nous conseillent vivement de planter très rapidement, c’est-à-dire la semaine prochaine, tant que la terre n’est pas encore très dure.

- Combien nous sommes pour planter ?

Venez nombreux avec vos idées ! Parlez-en autour de vous avec vos collègues !

Le 29 juin 2023 aura lieu à l'ENS-Lyon la sixième  Journée Parité 2023 organisée par Olga Paris-Romaskevich, Frédérique Bienvenüe, Vincent Borrelli, Jean-René Chazottes, Claire Lacour, Bertrand Rémy.

Cette 6ème Journée Parité s'adresse à celles et ceux intéressé·e·s qui veulent réfléchir et échanger sur les manières d'agir pour une communauté mathématique inclusive, apaisée et ouverte. Nous espérons qu'elle vous apportera du soutien, des outils, des idées et de belles rencontres pour encore plus de sens dans cette aventure collective.

The 12th CPHT Young Researchers Seminar will be held on April 19, 2023 at 3:00 p.m. in the Louis Michel Conference Room with two presentations :

Simon Pekar (Université de Mons) : Higher-spin gravity in flat space: old results and new developments
Arnaud Delfante (Université de Mons) : Weyl-Fefferman-Graham gauge and asymptotic symmetries

The seminar will be followed by a high tea.

The 11th CPHT Young Researchers Seminar will be held on April 14, 2023 at 3:00 p.m. in the Louis Michel Conference Room with two presentations :

Mikel Sanchez Garitaonandia (CPHT, CNRS, École Polytechnique) : Gravitational Waves from First Order Phase Transitions

Jong-Hyun Yoon (IJCLab, CNRS/IN2P3, Université Paris-Saclay) : Inflationary Big Bang Cosmology and Dark Matter

The seminar will be followed by a high tea.

Tuesday, April 4 at 14:00

Conference room Louis Michel (CPHT)

Erik Linnér (CPHT, École Polytechnique)

A theoretical description of the interplay of collective fluctuations in strongly correlates systems

Abstract: Correlated fermion systems often display complex phase diagrams with different competing orderings. A theoretical description of competing instabilities remains one of the major challenges of modern condensed matter physics. We introduce a multi-channel extension of the recently developed fluctuating field approach to tackle this problem, based on a variational optimization of a trial action that explicitly contains the leading fluctuation channels [1]. Application of the approach to extended Hubbard models captures the interplay of competing charge density wave, antiferromagnetic, s-wave superconductivity, and phase separation fluctuations [1,2]. For the case of the attractive model, our approach has allowed us to identify a novel phase that is characterised by the coexistence of s-wave superconductivity and phase separation [2]. Our findings resonate with previous observations of interplaying phase separation and superconducting phases in electronic systems, most importantly in high-temperature superconductors.

[1] E. Linnér, A. I. Lichtenstein, S. Biermann, E. A. Stepanov, Multi-channel fluctuating field approach to competing instabilities in interacting electronic systems, arXiv:2210.05540 (2022).

[2] E. Linnér, C. Dutreix, S. Biermann, E. A. Stepanov, Coexistence of s-wave superconductivity and phase separation in the half-filled extended Hubbard model with attractive interactions, arXiv:2301.10755 (2023).

Tuesday, March 21 at 14:00

Conference room Laurent Schwartz (CMLS)

Dario Fiore Mosca (CPHT)

Multipolar magnetism in 5d osmate double perovskites

Abstract: The Spin-Orbit Coupling effect plays a crucial role in the correlated electron physics of 5d transition metal oxides, enabling the formation of unique magnetic phases involving high-rank magnetic multipoles. We show that the 5d1 osmate double perovskite Ba2NaOsO6 and 5d2 Ba2MOsO6 (M = Mg, Ca, Zn) are ideal for exploring such physics. They display strong interconnection between the structural, electronic, and magnetic degrees of freedom that gives rise to multipolar interactions, multipolar order, and spin-orbit polarons.

The 10th CPHT Young Researchers Seminar will be held on March 17, 2023 at 3:00 p.m. in the Louis Michel Conference Room with a presentation given by :

Jack Holguin (CPHT, CNRS, École Polytechnique) : Energy Correlators for Collider QCD

The seminar will be followed by a high tea.