- Déc 20 2023
- 11h00 - 12h30
Séminaire – Eric Bousquet (Université de Liège)
Eric Bousquet (Université de Liège) donnera un séminaire le 20 Décembre à 11h dans l’Auditorium de TRT.
Titre: Ferroelectricity, chirality, spin-orbit coupling and cavity states in Pb5Ge3O11
Pb5Ge3O11 is a room temperature ferroelectric which is also known to be gyroelectric, i.e. its natural optical activity can be reversed under an applied electric field during the ferroelectric domain switching. It is recently re-explored because of his unique topological domains coming from the uniaxial ferroelectricity and head-to-head/tail-to-tail domain walls. Here, we will show that Pb5Ge3O11 is even more versatile than known so far. By scrutinizing this crystal with first-principles DFT calculations, we will first show that the ferroelectric character belongs to the so-called hyperferroelectrics where the polar distortions couple non-linearly and cooperatively with the internal degrees of freedom of the paraelectric phase (i.e. the invariant modes). We will also quantify the origin of the structural chirality of the low symmetry ferroelectric phase and, hence, we will explain why the crystal is gyroelectric. At last, we will show that the ferroelectric energy landscape is surprisingly and strongly renormalized by the spin-orbit coupling and where it is the non-linear coupling that is the most renormalized. In trying to understand why the spin-orbit coupling is so important in this non-magnetic crystal, we will highlight that it is coming from the empty 6p orbitals of the Pb atoms that localize in the natural hollow tube present in this crystal. These states form surprising cavity states that makes the ferroelectricity very robust against electron doping.