Induced Functionalities by Symmetry Breaking

Symmetry lies at the heart of the laws of nature and determines material properties at the fundamental level. We all know that breaking the inversion symmetry is directly mapped into materials properties by inducing a plethora of effects such as dielectric polarisation along with pyro- and ferroelectricity, piezoelectricity, bulk photovoltaic effect, electro-optic effect and second harmonic generation, etc. Material symmetry in chiefly determined by its pristine crystallographic structure, but external stimuli can also lower symmetry or even break the inversion symmetry. A well-known example of such stimulus is the strain gradient that breaks the inversion and induces electric polarisation in any material, including centrosymmetric materials, by the so-called flexo-electric effect.

In this talk, I will focus on inducing the effects associated with inversion symmetry breaking in native centrosymmetric materials. I will show that strain gradients not only induce electric polarisation but also convert any semiconductor in a photovoltaic/photogalvanic generator by the flexo-photovoltaic effect.

Similarly, built-in electrical fields within ubiquitous Schottky contacts break the symmetry at the interface inducing piezo- and pyroelectricity with completely different tweaking parameters than classical piezo- and pyroelectrics. I will also show that ferroelectric polarisation breaks locally the symmetry in contiguous materials, especially magnetic oxides, inducing novel magnetic phases such as spin crystals.

About the speaker

Professor Marin Alexe received his PhD degree in 1995 from the Institute of Atomic Physics, Bucharest, Romania. He has been appointed as Chair of Functional Materials at the University of Warwick after spending about 18 years at the Max Planck Institute of Microstructure Physics-Halle (1996-2013). His research interest is physics and engineering of complex oxide thins films for information technology and integration of functional materials for oxide electronics. He was recently awarded Wolfson Research Merit and Theo Murphy“Blue Sky”Awards of the Royal Society and the Alexander von Humboldt Research Award.

https://warwick.ac.uk/fac/sci/physics/research/condensedmatt/functionalelectronicmaterials/