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Dynamical Correlations and Order in Magic-Angle Twisted Bilayer Graphene
No full textInternational audienceThe interplay of dynamical correlations and electronic ordering is pivotal in shaping phase diagrams of correlated quantum materials. In magic-angle twisted bilayer graphene, transport, thermodynamic, and spectroscopic experiments pinpoint a competition between distinct low-energy states with and without electronic order, as well as between localized and delocalized charge carriers. In this study, we utilize dynamical mean-field theory on the topological heavy fermion model of twisted bilayer graphene to investigate the emergence of electronic correlations and long-range order in the absence of strain. We contrast moment formation, Kondo screening, and ordering on a temperature basis and explain the nature of emergent correlated states based on three central phenomena: (i) the formation of local spin and valley isospin moments around 100 K, (ii) the ordering of the local isospin moments around 10 K preempting Kondo screening, and (iii) a cascadic redistribution of charge between localized and delocalized electronic states upon doping. At integer fillings, we find that low-energy spectral weight is depleted in the symmetric phase, while we find insulating states with gaps enhanced by exchange coupling in the zero-strain ordered phases. Doping away from integer filling results in distinct metallic states: a “bad metal” above the ordering temperature, where scattering off the disordered local moments suppresses electronic coherence, and a “good metal” in the ordered states with coherence of quasiparticles facilitated by isospin order. This finding reveals coherence from order as the microscopic mechanism behind the Pomeranchuk effect observed experimentally by Rozen [] and by Saito []. Upon doping, there is a periodic charge reshuffling between localized and delocalized electronic orbitals leading to cascades of doping-induced Lifshitz transitions, local spectral weight redistributions, and periodic variations of the electronic compressibility ranging from nearly incompressible to negative. Our findings highlight the essential role of charge transfer, hybridization, and ordering in shaping the electronic excitations and thermodynamic properties in twisted bilayer graphene and provide a unified understanding of the most puzzling aspects of scanning tunneling spectroscopy, transport, and compressibility experiments. Published by the American Physical Society 202
Visible-Light-Driven Carbon Dioxide Reduction Catalyzed by Iron Schiff-Base Complexes
No full textInternational audienceLight-dependent reduction of carbon dioxide (CO 2 ) can be sustainably developed using non-expensive and abundant molecular catalysts and inorganic photosensitizers, based on non-noble metals. The photoreduction of CO 2 catalyzed by a series of eleven metal-salophen complexes, based on variously functionalized salophen ligands, has been investigated using a Cubased photosensitizer, [Cu I (bathocupoine)(xantphos)], for light-harvesting. This provides one of the currently few fully earth-abundant systems for efficient CO 2 reduction driven by visible light.Using 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as the sacrificial reductant in acetonitrile/triethanolamine solution, a maximum turnover number for CO production of 900-1600, a maximum initial turnover frequency of 1300-1700 h -1 with 93-96 % CO:H 2 selectivity, and a high quantum yield of 12-15% (at 420 nm) were achieved with Fe-based complexes. Thorough photophysical studies coupled to DFT calculations allowed reaction intermediates tracking and provided insights into the reaction mechanism.</div
Bilan et retours d'expérience du programme Archéologie trans-himalayenne: mouvements de population et interactions matérielles (2019-2024)
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Actualité de la recherche sur les peintures murales du Tibet: acquisitions récentes de la Bibliothèque d’Etudes Tibétaines
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Introduction aux manuscrits littéraires du pays de Chu (4ème et 3ème siècles av. n. è.)
No full textMasterCette série de conférences a pour objet les manuscrits philosophiques et littéraires de l’époque des Royaumes combattants (481-221 av. n. è.), qui furent exhumés au cours des dernières décennies dans des tombes de l’ancien royaume de Chu. La grande majorité du contenu de ces manuscrits n'a pas été transmis par la tradition lettrée, éclairant ainsi d'un jour nouveau l'histoire intellectuelle de la Chine ancienne. Après une séance introductive consacrée au contexte de découverte et aux spécificités de ces manuscrits sur fiches de bambou, nous présenterons les principaux corpus découverts à ce jour et commenterons plusieurs passages extraits de ces écrits inédits
Formation of 3-Alkynylidenephthalides by Gold(I)-Catalyzed Alkynylative Cyclization of o-Alkynylbenzoic Acids under Visible Light Irradiation
No full textInternational audienceHerein, we report a Csp2–Csp cross-coupling process involving the merger of gold catalysis and visible light photocatalysis leading to the alkynylative cyclization of o-alkynyl benzoic acids. The corresponding and previously undescribed alkynylidenephthalide products were obtained as mixtures of E:Z isomers. The key C–C bond formation is based on the photoactivation of the oxidative addition of an alkynyliodide to a vinylgold(I) intermediate resulting from an initial 5-exo-dig cyclization pathway, as supported by mechanistic studies including DFT calculations
Commentary and Exegesis in the Pre-Modern, Modern, and Contemporary Chinese Worlds
No full textInternational audienceDespite its centrality and its impact from a historical perspective, commentary is usually considered a tool for deciphering great works or as a faint trace of intellectual activity. Except for a few instances in the field of philosophy, it has been reduced to an ancillary status and denied that of a text per se. This introduction presents the framework in which the project of this special issue developed, the questions that were raised, and the key elements that characterise commentaries and that ap-peared through the project.儘管註釋在歷史上發揮著關鍵作用，但通常僅被視為理解古典作品的輔助工具，或是反映古人學術活動的細微痕跡。除哲學領域的少量研究外，註釋作為獨立文本的學術價值一直未得到充分重視，更多地被輕視為輔助工具。引言將介紹本專刊的研究框架和探討的核心問題，並揭示註釋在此過程中展現的獨特特質以及學術意義
A search using GEO600 for gravitational waves coincident with fast radio bursts from SGR 1935+2154
No full textInternational audienceThe magnetar SGR 1935+2154 is the only known Galactic source of fast radio bursts (FRBs). FRBs from SGR 1935+2154 were first detected by CHIME/FRB and STARE2 in 2020 April, after the conclusion of the LIGO, Virgo, and KAGRA Collaborations' O3 observing run. Here we analyze four periods of gravitational wave (GW) data from the GEO600 detector coincident with four periods of FRB activity detected by CHIME/FRB, as well as X-ray glitches and X-ray bursts detected by NICER and NuSTAR close to the time of one of the FRBs. We do not detect any significant GW emission from any of the events. Instead, using a short-duration GW search (for bursts 1 s) we derive 50% (90%) upper limits of () erg for GWs at 300 Hz and () erg at 2 kHz, and constrain the GW-to-radio energy ratio to . We also derive upper limits from a long-duration search for bursts with durations between 1 and 10 s. These represent the strictest upper limits on concurrent GW emission from FRBs
Une arche animée : littérature et zoopoétique
No full textInternational audienceWhether it's drowning in water or stranded on an arid wasteland, the ark of living creatures is more endangered than ever, in ways that are unevenly critical depending on the species, socio-cultural status or location. Concerned about this depopulating ark, zoopoetics refers to literary studies that pay attention to the fantastic diversity of intertwinings between the elements and the animate (including human beings), studying in particular the insistent presence as well as the furtive passage of animals in our texts and in our minds. For zoopoetics, living beings and nature are not just another theme : they underpin and run through our culture, even if this has been forgotten or denied. Challenging the dissociation between nature and culture, or confronting its disastrous effects, many writers renew lexicons and deconstruct syntax to give an account of the sensitive and affective worlds of animals. This eminently poetic (by which we mean creative) undertaking involves studying language and its connections: simply recounting the lives of animals or our relationships with them by idealising or simplifying them for ‘the good of the cause’ is tantamount to perpetuating structures of thought and expression that have led to the ecological disaster in the first place.Qu'elle prenne l'eau à en couler ou s'échoue sur une terre aride et désolée, l'arche des vivants est plus que jamais en péril, de façon inégalement critique selon les espèces, les statuts socio-culturels ou les lieux. Soucieuse de cette arche qui se dépeuple, la zoopoétique désigne les études littéraires attentives à la fantastique diversité des enroulements entre les éléments et les animés (humains compris), en étudiant notamment la présence insistante tout comme le passage furtif des bêtes dans nos textes et dans nos têtes. Pour la zoopoétique, les vivants et la nature ne sont pas des thèmes parmi d'autres, puisqu'ils fondent et traversent notre culture, même si on l'a oublié ou dénié. Nombreux sont en effet les écrivaines et les écrivains qui, récusant la dissociation entre nature et culture, ou en affrontant les effets désastreux, rénovent les lexiques et déconstruisent la syntaxe pour rendre compte des mondes sensibles et affectifs animaux. Cette entreprise éminemment poétique (entendez créatrice) passe donc par un travail sur le langage et ses adhérences : se contenter de raconter la vie des bêtes ou nos relations avec elles en les idéalisant ou en les simplifiant pour « la bonne cause » revient en effet à reconduire des structures de pensée et de dire qui ont précisément mené à la catastrophe écologique