SFP Alpes

Doru C. LUPASCU (Institute for Materials Science and CENIDE - Faculty of Engineering, University of Duisburg-Essen)
2026-02-06 10:30 - 12:30 (Europe/Paris) | ILL – Salle de Séminaire (110-111), ILL 50 71 avenue des Martyrs, Grenoble, 38042, France
Hyperfine Interactions as a Probe in Solids : The Example of a Multiferroic System : Bismuth Ferrite
Hyperfine interactions denote the coupling of the wave functions of nuclear states to the electronic shell of the atom. This coupling is a correction term to the energy of a nuclear state and equally so in reverse manner for the electronic shell of the atom.
Like nuclear magnetic resonance or Mössbaer spectroscopy, the nuclear perturbed gamma-gamma-angular correlation spectroscopy (PAC) investigates this energetic modification of the nuclear state. For sufficiently high nuclear spin value, magnetic interactions as well as quadrupole interactions become accessible. The beauty of the method is its highly local character in the crystal lattice. It directly monitors fields at a particular lattice or defect site. Similar is true for molecules.
Bismuth ferrite is a perovskite crystal exhibiting magnetic and electric ordering phenomena. It is antiferromagnetic and a very good ferroelectric. We used several probe atoms that offer suitable nuclear gamma-gamma cascades to understand these two ordering phenomena in the identical crystal and their coupling. Different from the long term belief, we proved that there is no magnetoelectric coupling in this crystal.
The presentation will introduce the measurement method, and the material system and display how it can be used to investigate solids in a very local manner.
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Hanno Filter (College 3 Secretary)
External visitors may ask for a site access to tellier(at)ill.fr
Zoom link : https://ill.zoom.us/j/98964195699?pwd=[REDACTED] – Password : [REDACTED]

William FAUGNO (LKB / Collège de France)
2026-02-06 11:00 - 12:00 | LPMMC – salle Roger Maynard (G421), CNRS - LPMMC 25 avenue des Martyrs, Grenoble, 38042, France
Quantum Many-Body Scars in the Presence of Density-Difference-Dependent Hopping
Résumé :
It has been observed that isolated quantum systems often still produce measured values consistent with thermalization. This is unexpected due to the lack of a notion of chaos or ergodicity and the unitary dynamics of the quantum theory which is at its core linear. The conditions under which we can expect isolated quantum systems to thermalize were laid out in the eigenstate thermalization hypothesis (ETH), which has generally been found to hold in a variety of systems. Still, notable violations of the ETH have been identified where a seemingly chaotic many-body quantum system exhibits some nonthermal behavior. In this talk, I will introduce the concept of quantum many-body scars (QMBS), a phenomenon in which a small subset of eigenstates violates the ETH and promote nonthermal dynamics. I will then present theoretical results on a bosonic Hamiltonian with a density-dependent hopping and describe two distinct mechanisms for scar formation that arise in this model. These mechanisms provide insight into the conditions under which QMBS can be expected to occur.
Contact : serge.florens@neel.cnrs.fr

Kei YAMAMOTO (Advanced Science Research Center, Japan)
2026-02-06 11:00 - 12:00 | CEA – Salle de Séminaire IRIG (1005 – 445), Laboratoire Irig/Spintec, salle de séminaire 445, bâtiment 1005, CEA-Grenoble, Grenoble
Spin-wave spectrum in a ferromagnetic disk
Abstract :
Angular momentum transfer in all forms contributes to the loss of information carried by dynamical spin polarisations and constitutes an important fundamental problem in spintronics. In this talk, we present a detailed microwave spectrum measurement of magnetic excitations in an Yttrium Iron Garnet disk, and how one can make sense of the multitudes of spectral lines and their magnetic field dependence theoretically. We explain how the axial symmetry of the setup leads to labelling of modes in terms of the conserved total angular momentum of the spin waves, The frequency spectrum in the saturated state is compared to analytical solutions for pure exchange as well as pure dipolar models under certain limits where different types of spectral degeneracy occur. The experimental result shows splittings of those degenerate modes, and we discuss possible interpretations in relation to angular momentum transfer between its different forms.
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More information :https://www.spintec.fr/seminar-spin-wave-spectrum-in-a-ferromagnetic-disk/​​​
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Visioconference :https://univ-grenoble-alpes-fr.zoom.us/j/98769867024?pwd=[REDACTED]​​
