Colloquium: Peter Littlewood, University of Chicago
Abstract: Ten of the 32 crystal point groups have symmetries that allow a spontaneous electrical polarization and therefore an internal electric field. In practice this field is screened by charged debris on the surface of acrystal and so is not observable macroscopically, but it was noted by Theophrastus (c 300 BCE) that on heating tourmaline (which we now know to be polar) it would attract small pieces of dust. With the 19th century understanding of electricity this was dubbed pyroelectricity, and we now call such materials polar. Later, piezo electricity, when a reversible polarization is induced by elastic strain was discovered by Jacques and Pierre Curie. In 1920 Valasek in Minnesota, studying Rochelle salt, discovered that the direction of the polarization can stable but hysteretic, and switched by the application of an external electric field. Such materials we now term ferroelectric,in analogy to ferromagnetism.
While an ancient topic it has many modern resonances.Ferroelectric and piezoelectric materials are important technologically. Themodern definition of polarization distinguishes bulk and surface origins through what we now call a topological term. The phase transition from para electric to ferroelectric has been presented both as a paradigm for “displacive” (i.e. nearly mean field like) versus“order-disorder” (like a local-moment ferromagnet) phase transitions. Thezero-temperature phase transition (tuned e.g. by pressure in SrTiO3)is an opportunity to study quantum critical phenomena (QCP) in a simple bosonic system yet exhibits a puzzling phenomenology. Furthermore, by electronic doping in the vicinity of the QCP we observe a robust superconducting dome at very low carrier densities.
After a historical tour, this talk will focus on the role of elastic degrees of freedom in mediating long-range interactions between dipoles,with a particular focus on SrTiO3.
J Fousek, JosephValasek and the discovery of ferroelectricity, Proceedings of 1994 IEEEInternational Symposium on Applications of Ferroelectrics 1994
GG Guzmán-Verri, RT Brierley, PB Littlewood Nature 576,429-432 (2019)
SAJ Kimber et al., arXiv:2202.05565
GG Guzmán-Verri, CH Liang, PB Littlewood, arXiv:2205.14171
CS Kengle et al.,arXiv:2210.15026
L Lin, PB Littlewood, A Edelman, arXiv:2111.12250