Flat Club - Frédéric Mila, EPFL

06.12.2024 12:30 – 14:00

Artificial 2D magnets, frustrated Ising models, and exotic Kasteleyn transition
Frédéric Mila, EPFL

Over the last 20 years, a lot of progress has been made in the realisation of 2D arrangements of magnetic islands. The moment of each island must point along a local axis, and the system can be described by interacting Ising spins. If the magnetic moments are parallel to the plane, the resulting model is some kind of spin-ice model with local constraints at vertices, while if they point perpendicular to the plane the system can be described by an antiferromagnetic model with long-range couplings. In this talk, motivated by the experimental realisation of an Ising kagome antiferromagnet in the group of Laura Heydermann at PSI, I will report on the investigation of the J1-J2-J3 Ising model on the kagome antiferromagnet. After a description of the rich zero-temperature phase diagram of that model, with the surprising result that couplings up to third neighbours are in most cases not sufficient to completely lift the ground state degeneracy of the kagome antiferromagnet, I will concentrate on the thermal properties of one of these phases. I will show that, in the limit of strong first and third neighbor couplings, the physics is Kasteleyn like, with the condensation of linear defects in a fluctuation-free low temperature phase. However, the transition takes an exotic form in that case, some kind of quantized Kasteleyn transition, with an infinite sequence of first-order transitions between phases that can be characterised by a topological invariant.

Lieu

Bâtiment: Ecole de Physique

Auditoire Stueckelberg
Pizza: 12:30, Start discussion: 13:00

entrée libre