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DTSTART;TZID=Europe/Paris:20260612T110000
DTEND;TZID=Europe/Paris:20260612T120000
DTSTAMP:20260620T114824
CREATED:20260604T132045Z
LAST-MODIFIED:20260604T132045Z
UID:10000183-1781262000-1781265600@sfp-alpes.fr
SUMMARY:Benjamin LENZ (IMPMC)
DESCRIPTION:Spectroscopic signatures of spin-polarons in quasi two-dimensional correlated materials\nRésumé : \nThe motion of a single hole in a two-dimensional antiferromagnet can lead to the formation of a low-energy quasiparticle\, a so-called spin-polaron\, which amounts to a bound state of the doped hole and a spin flip. In this talk\, I will first introduce the notion of spin-polarons and then discuss spectroscopic signatures of this quasiparticle at the example of two different material classes which both host quasi two-dimensional low-energy physics in their correlated electronic structure.\nIllustrated by the Na-doped oxychloride Ca2CuO2Cl2\, we will see how the spin-polaron gives rise to “kink” and “waterfall” features in the spectral function of hole-doped cuprates. Employing a numerical workflow comprising density functional theory and cluster dynamical mean-field theory\, we will discuss these features in comparison to measurements obtained from angle-resolved photoemission spectroscopy. As a second example\, we will see that spin-polaron physics is also relevant in two prototypical iridates\, (Ba\,Sr)2IrO4\, which host an exotic spin-orbital entangled jeff=1/2 ground state. In particular\, the characteristic two-peak structure of their optical absorption and optical conductivity curves will be revisited and interpreted in the light of these coherent low-energy quasiparticles. \nB. Bacq-Labreuil et al.\, Phys. Rev. Lett. 134\, 016502 (2025)\nF. Cassol et al.\, arXiv:2509.20337; accepted in Phys. Rev. B (2026) \n_ \nContact : serge.florens@neel.cnrs.fr
URL:https://sfp-alpes.fr/event/benjamin-lenz-impmc/
LOCATION:LPMMC – salle Roger Maynard (G421)\, CNRS - LPMMC 25 avenue des Martyrs\, Grenoble\, 38042\, France
CATEGORIES:Séminaire
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DTSTART;TZID=Europe/Paris:20260612T110000
DTEND;TZID=Europe/Paris:20260612T120000
DTSTAMP:20260620T114824
CREATED:20260604T142423Z
LAST-MODIFIED:20260604T142423Z
UID:10000187-1781262000-1781265600@sfp-alpes.fr
SUMMARY:Alexandra COLIN (CEA-Irig/LPCV)
DESCRIPTION:Dynamics and Scaling of Competitive Actin Architectures\nRésumé : \n\nCells constantly experience environmental changes requiring a fast adaptation of their different actin structures. However\, the mechanisms governing the size and dynamics of these multiple actin structures remain unknown. Decoupling the various parameters that would provide a complete understanding of these mechanisms is very complicated in a cellular context. This is why we have developed a bottom-up approach to identify the key molecular mechanisms that determine the size and coexistence of multiple competing actin architectures. We used a reconstituted system consisting of purified proteins and substrates to localize actin polymerization in microwells\, enabling us to work with a limited number of components. With this system\, we reconstituted several dynamic actin architectures\, competing for a limited pool of protein\, over a period of multiple hours. This allowed us to gain key insights into physiological functions related to actin turnover. I will show how we used this system to study the limits of scaling in dynamic structures\, as well as the limits of coexistence in actin networks under resource-limited conditions. Finally\, I will show how we can recapitulate these results in a complementary cellular system\, in which we have demonstrated that an increase in spreading area leads to a decrease in overall turnover\, due to a predominance of structures with low turnover.​​​​​\n​\n\n\n\nLes séminaires et soutenances sont ouverts à tous\, notez toutefois que l’accès au campus EPN nécessite un avis de rendez-vous. Merci de remplir ce formulaire  et de l’adresser\, plus de 48h à l’avance\, à ce contact.\nPensez à vous munir d’une pièce d’identité le jour de votre visite.
URL:https://sfp-alpes.fr/event/alexandra-colin-cea-irig-lpcv/
LOCATION:IBS – Salle des séminaires\, IBS 71 avenue des Martyrs\, Grenoble\, 38042\, France
CATEGORIES:Séminaire
ORGANIZER;CN="IRIG - CEA":MAILTO:odile.rossignol@cea.fr
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260612T140000
DTEND;TZID=Europe/Paris:20260612T160000
DTSTAMP:20260620T114824
CREATED:20260604T141732Z
LAST-MODIFIED:20260604T141732Z
UID:10000186-1781272800-1781280000@sfp-alpes.fr
SUMMARY:Soutenance de Thèse de Giovanni OLIVETTI (CEA-Irig / Spintec)
DESCRIPTION:Angular Momentum Transfer Between Waveforms in Axisymmetric Geometries\nRésumé : \nThis thesis investigates the role of angular momentum transfer in the coupling between elastic and spin excitations in magneto-mechanical systems. \nIn axisymmetric geometries\, rotational invariance provides the natural framework for the conservation of total angular momentum[1]. In such a case\, this quantity unambiguously labels the eigenmodes of the system and constrains their coupling to an external excitation through well-defined selection rules[2]. The manuscript develops this physical picture from a general perspective based on Noether’s theorem\, it introduces spin and orbital angular momentum contributions for a generic vector field and proposes an analytical description of magneto-elastic coupling in axisymmetric systems. \nThis framework is then applied to two complementary experimental platforms realized in the context of this doctoral work. The first combines chiral surface-acoustic excitations with a magnetic vortex texture in a patterned ferromagnetic disk. The second consists of partially suspended axisymmetric YIG microresonators\, designed to support both low-loss mechanical motion and confined spin dynamics within the same structure[3]. Together\, these two systems provide complementary routes to investigate how elastic and magnetic modes carrying angular momentum can be generated\, controlled\, and coupled in realistic devices. \nIn particular\, this work demonstrates the controlled excitation and optical mapping of a surface-acoustic vortex by means of spiral interdigitated transducers. It further addresses the stabilization of magnetic vortex textures in micrometer-scale ferromagnetic disks on anisotropic piezoelectric substrates\, as well as their positioning at the center of elastic rotation. The coupling strength in suspended axisymmetric YIG microresonators has been evaluated by comparing experimental data with theoretical modeling\, indicating a weak-coupling regime. Moreover\, the role of weak symmetry breaking has been discussed for the selective excitation of counter-propagating elastic modes that would otherwise be degenerate. \nThese developments establish several of the physical and technological conditions required to address experimentally the coupling of elastic and spin excitations carrying angular momentum. More broadly\, they outline a route toward magneto-elastic platforms in which symmetry can be used as a resource for selective excitation. In this perspective\, partially suspended magnetic microresonators may provide a promising route toward strong magnon-phonon coupling under geometrical and symmetry constraints directly relevant for coherent functionalities. In the longer term\, such systems could serve as building blocks for mode-selective transducers and hybrid architectures combining magnetic\, elastic\, and optical degrees of freedom\, with possible perspectives for microwave-to-optical coherent transduction[4]. \nReferences \n\nGaranin & Chudnovsky\, Phys. Rev. B 92\, 024421 (2015).\nAn et al.\, Phys. Rev. B 101\, 060407 (2020).\nHeyroth et al.\, Phys. Rev. Appl. 12\, 054031 (2019).\nEngelhardt et al.\, Phys. Rev. Appl. 18\, 044059 (2022). ​\n\n\n\nPlus d’information\n​ \nPour suivre la soutenance ​​​en visioconférence​ ​​: lien à venir\n\n\n\n\nAccess to the CNRS site is restricted. Please contact Olivetti Giovanni​  or Benjamin Pigeau at least 48h before the defense if you need an entry clearance. You just need to communicate your name and surname\, and you will receive the entry clearance by email.
URL:https://sfp-alpes.fr/event/soutenance-de-these-de-giovanni-olivetti-cea-irig-spintec/
LOCATION:CNRS – Bâtiment A\, CNRS - Institut Néel 25 avenue des Martyrs\, Grenoble\, 38054\, France
CATEGORIES:Soutenance,Soutenance de Thèse
ORGANIZER;CN="IRIG - CEA":MAILTO:odile.rossignol@cea.fr
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