Nanoscale ferroelectric phenomena

Main researchers: Marios Hadjimichael, Céline Lichtensteiger

Ferroelectrics are materials exhibiting a remanent polarisation that can be switched by applying an electric field. Ferroelectric materials are also pyroelectric and piezoelectric, and are useful for a wide range of technological applications, from non-volatile memories to sensors and actuators. These materials can consist of regions where the polarisation points in different directions, and each region with a uniform polarisation is called a domain. Recent years have seen a resurgence of interest in domains in ferroelectric materials, mostly due to the properties of their boundaries, domain walls. Domain walls have been shown to enhance the macroscopic properties of ferroelectrics, like the piezoelectric coefficient and the permittivity, but they also exhibit properties and symmetry different from the bulk. This recent interest has now created an entire new field of study in nanoscale ferroelectrics, termed domain wall nanoelectronics, with a worldwide scientific effort focused on understanding the structure and properties of domain walls, as well as utilizing them as novel components in electronic devices [1].

In Geneva, we have been working on the study of ferroelectric films and heterostructures for many years with a long-standing expertise in size effects and ferroelectric field effect [2], a well-established expertise in studying PbTiO3 films and multilayers on SrTiO3 [3], with detailed studies on the scaling of the ferroelectric polarization and the monodomain to polydomain transition in ultrathin PbTiO3 films [4], artificially induced hybrid improper ferroelectricity [5] and negative capacitance in PbTiO3/SrTiO3 superlattices [6].

Depolarising Field
The depolarization field arising from unscreened bound charges on the surface of the ferroelectric is generally strong enough to suppress the polarization completely and hence must be reduced in one of a number of ways [7].

[1]. G Catalan et al, Rev. Mod. Phys. 84, (2012)

[2]. C. H. Ahn et al, Science 80, (1997)

[3]. C. Lichtensteiger et al, Phys. Rev. Lett. 94, (2005)

[4]. C. Lichtensteiger et al, Nano Lett. 14, (2014)

[5]. E. Bousquet et al, Nature 452, (2008)

[6]. P. Zubko et al, Nature 534, (2016)

[7]. C. Lichtensteiger et al, Ch 12, Oxide Ultrathin Films, Science and Technology, Wiley (2011)