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
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).