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DTSTART;TZID=Europe/Paris:20260504T140000
DTEND;TZID=Europe/Paris:20260504T150000
DTSTAMP:20260502T002001
CREATED:20260424T081257Z
LAST-MODIFIED:20260424T081257Z
UID:10000128-1777903200-1777906800@sfp-alpes.fr
SUMMARY:Maxime LUCAS (CY Cergy Paris Université)
DESCRIPTION:Non-collinear magnetism in monolayer and magic-angle twisted bilayer graphene\nRésumé : \nRecent studies of twisted bilayer graphene (or other 2D materials) have been stimulated by the discovery of correlations between electronic flatband states due to a moiré pattern [1]. It is shown experimentally and theoretically that the filling of the flat bands affects their correlation and magnetic properties significantly.\nOn the other hand\, the effect of doping on a simple graphene layer is still unclear. Indeed\, its half-filled case is well known [2]\, but unlike other lattices [3] its magnetic properties beyond half filling are mostly unexplored\, except at 1/4 doping [4] i.e when the Fermi energy is set inside of a Van Hove singularity associated to a flatband.\nIn this talk\, I will first present our analysis of graphene magnetism using a combination of the Hubbard model and Hartree-Fock Mean Field Theory (MFT). We work at density values around 1/4 doping (average number of electrons per site Ne=0.75) as it puts the system right into one of the Van Hove singularities found in graphene’s density of states\, giving rise to interesting magnetic properties. We present an interaction-density phase diagram and its associated magnetic orders\, described by their band structure and spin structure factor [5].\nI will then talk about magic-angle twisted bilayer graphene\, to which we applied the same MFT method. While still a work in progress\, I will present the current results we obtained on a Moiré lattice for various values of interaction and flat-band filling\, revealing exotic spin textures such as an antiferromagnetic triangular order on the Moiré scale.\n[1] Y. Cao et al.\, Nature 556\, 43 (2018); Nature 556\, 80 (2018).\n[2] M. Raczkowski et al.\, Phys. Rev. B 101\, 125103 (2020)\, and Refs. therein.\n[3] R. Scholle et al.\, Phys. Rev. B 108\, 035139 (2023)\n[4] S. Jiang\, A. Mesaros\, Y. Ran\, Phys. Rev. X 4\, 031040 (2014)\n[5] M. Lucas\, A. Ralko\, A. Honecker\, G. Trambly de Laissardière\, arXiv:2511.22714 (2025) \n_ \nContact : andrew.fefferman@neel.cnrs.fr
URL:https://sfp-alpes.fr/event/maxime-lucas-cy-cergy-paris-universite/
LOCATION:CNRS – Salle Louis Weil (E424)\, CNRS - Institut Néel 25 avenue des Martyrs\, Grenoble\, 38042\, France
CATEGORIES:Séminaire
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DTSTART;TZID=Europe/Paris:20260511T140000
DTEND;TZID=Europe/Paris:20260511T150000
DTSTAMP:20260502T002001
CREATED:20260424T124347Z
LAST-MODIFIED:20260424T124347Z
UID:10000132-1778508000-1778511600@sfp-alpes.fr
SUMMARY:Bo PENG (Cavendish Laboratory\, University of Cambridge)
DESCRIPTION:Designing molecular quantum materials from first principles\nRésumé : \nQuantum materials provide the basic building blocks for quantum hardware\, but it remains challenging to design robust\, tuneable and scalable material platforms. In this talk\, I will present strategies for engineering quantum materials based on molecular building blocks using first principles calculations. Molecules provide more tuneable building blocks than atoms [1\,2]\, which can self-assemble into larger structures [3\,4] with richer structural behaviours [5] for practical quantum devices. Using pure-carbon fullerene molecules that were believed to be non-magnetic [6]\, we show that magnetism in this material family can be induced purely by symmetry [7]. We can then use this pure-carbon magnetic material to design various quantum platforms\, based on experimentally synthesised monolayers [8\,9]\, to realise exotic quantum phenomena such as ferromagnetic Chern insulators [10]\, antiferromagnetic spin chain [11]\, altermagnetism and quantum spin liquid [12]\, as well as magnetoelectrics where spins can be controlled by electric fields. If time allows\, I will also discuss my ongoing research that combines both atomic and molecular building blocks. With this approach\, we can unlock even more exciting applications such as portable quantum timekeeping\, robust quantum sensing\, and programmable quantum simulations.\n\nReferences:\n[1] BP*. Journal of the American Chemical Society 144\, 19921 (2022).\n[2] J. Wu & BP*. Journal of the American Chemical Society 147\, 1749 (2025).\n[3] BP*. Nano Letters 23\, 652 (2023).\n[4] BP* & M. Pizzochero*. ACS Nano 19\, 29637 (2025).\n[5] A. Shaikh\, J. Wu & BP*. Physical Review Letters 135\, 126103 (2025).\n[6] T. L. Makarova\, et al. Nature 413\, 716 (2001) [Retracted].\n[7] J. Wu\, L. W. Pingen\, T. K. Dickens & BP*. arXiv:2508.18125.\n[8] L. Hou\, et al. Nature 606\, 507 (2022).\n[9] E. Meirzadeh\, et al. Nature 613\, 71 (2023).\n[10] L. W. Pingen\, J. Wu & BP*. arXiv:2508.19849. [Physical Review Letters\, in revision]\n[11] BP* & M. Pizzochero*. arXiv:2508.18849. [Nano Letters\, in press]\n[12] J. Wu\, A. Sanders\, R. Yuan & BP*. arXiv:2508.21056.\n\n_\n\nContact : andrew.fefferman@neel.cnrs.fr
URL:https://sfp-alpes.fr/event/bo-peng-cavendish-laboratory-university-of-cambridge/
LOCATION:CNRS – Salle Louis Weil (E424)\, CNRS - Institut Néel 25 avenue des Martyrs\, Grenoble\, 38042\, France
CATEGORIES:Séminaire
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