CHARLA IFLYSIB VIRTUAL Viernes 23/09 · Ludovic Jaubert · «Reentrance in frustrated systems»

Título: Reentrance in frustrated systems

Expositor: Ludovic Jaubert – CNRS, Université de Bordeaux, LOMA, Talence, France

Fecha: Viernes 23/09/2022 – 10:30 hs

Resumen:

Upon cooling, our intuition tells us that a system shall become more ordered: for example from liquid to solid, or from paramagnetic to ferromagnetic. However, exceptions exist, and a disordered phase sometimes reappears at lower temperatures. This is the phenomenon of reentrance, which is a recurring theme found in disparate physical systems, from condensed matter to black holes. In addition to temperature, reentrance can also take place upon variation of other external parameters; e.g. a system might be paramagnetic at low and high fields, but magnetically ordered at intermediate values.

In this seminar, we will present a historical and general introduction to the phenomenon of reentrance, both in theory and experiments. In particular, reentrance seems to be a common property of frustrated systems in a magnetic field. However, a generic understanding of its underlying mechanism is still lacking. Here, we will explain one of its microscopic mechanism, taking the example of the antiferromagnetic pyrochlore Er₂Sn₂O₇. Monte Carlo simulations reproduce the multiple instances of reentrance measured experimentally via state-of-the-art heat capacity measurements of Er₂Sn₂O₇, in three different field directions. Analysing these simulations in light of classical linear spin-wave expansions, we will show that the origin of this reentrance is linked to soft-mode excitations attached to zero-temperature phase transitions, and discuss its consequence.

Ref: Yahne, Pereira, Jaubert, Sanjeewa, Powell, Kolis, Xu, Enjalran, Gingras & Ross, Understanding reentrance in frustrated magnets: The case of the Er₂Sn₂O₇ Pyrochlore, Phys. Rev. Lett. 127, 277206 (2021).